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THE   CHAUTAUQUA   LITERARY   AND  SCIEN- 
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Cbautauqua  IReaDing  Circle  ^Literature 

A  |  .   I 

STUDY  OF  THE  SKY 


BY 


HERBERT  A.   HOWE,  A.M.,  Sc.D., 


Director  of  the  Chamberlin  Observatory,  University  of  Denver ;   author  of 
"Elements  of  Descriptive  Astronomy." 


MEADVILLE  PENNA 
FLOOD  AND  VINCENT 
Cfoe 


NEW  YORK  :  CINCINNATI  :  CHICAGO  : 

150  Fifth  Avenue.      222  W.  Fourth  St.      57  Washington  St. 
1896 


Copyright,  1896 
By  FLOOD  &  VINCENT 


The  Chautauqua- Century  Press,  .Meadville,  Pa.,   U.  S.  A. 
Electrotyped,  Printed,  and  Bound  by  Flood  &  Vincent. 


ASTRONOMY 
LIBRARY 


TO    HUNDREDS    OF    MY    PUPILS, 

WHOSE  STEADFAST   DEVOTION 

TO  THEIR   DAILY   TASKS 

IS  A   DELIGHTFUL   MEMORY, 

THIS   BOOK   IS 

AFFECTIONATELY  DEDICATED 


The  required  books  of  the  C.  L.  S.  C.  are  recommended  by  a 
Council  of  six.  It  must,  however,  be  understood  that 
recommendation  does  not  involve  an  approval  by  the  Coun- 
cil, or  by  any  member  of  it,  of  every  principle  or  doctrine 
contained  in  the  book  recommended. 


PREFACE. 

ASTRONOMY  is  at  once  the  most  ancient  and  the 
noblest  of  the  physical  sciences.  For  thousands  of 
years  successive  generations  of  men  have  gazed  with  ad- 
miration and  delight  at  the  brilliant  orbs  which  glitter  in 
the  diadem  of  night.  The  shining  constellations,  the 
roving  planets,  the  ever-changing  moon,  the  splendid 
Galaxy,  a  celestial  river  bedded  by  suns  and  banked  by 
the  ether,  all  these  display  their  beauties  before  the 
ravished  eye. 

"The  sky 

Spreads  like  an  ocean  hung  on  high, 
Bespangled  with  those  isles  of  light 
So  wildly,  spiritually  bright. 
Who  ever  gazed  upon  them  shining, 
And  turned  to  earth  without  repining, 
Nor  wished  for  wings  to  flee  away, 
And  mix  with  their  eternal  ray?" 

To  the  study  of  these  inspiring  objects  our  book  is 
devoted.  Their  story  is  told  with  plainness  and  sim- 
plicity. The  standpoint  adopted  is  that  of  the  astron- 
omer, who  observes,  records  what  he  sees,  studies  his 
observations,  digs  out  the  truths  which  they  contain, 
and  weaves  them  into  laws  and  theories  which  embrace 
the  visible  universe,  reaching  from  unknown  depths  of 
past  ages  up  to  unmeasured  heights  of  futurity. 

The  historical  development  of  the  science  is  sketched. 
An  explanation  of  the  apparent  daily  motion  of  the 
heavens  is  given.  The  chief  constellations  are  set  forth 
in  detail,  that  the  learner  may  have  ample  guidance  in 


vi  Preface. 

his  endeavors  to  become  acquainted  with  them.  The 
reader  is  introduced  to  the  astronomer,  inspects  an  ob- 
servatory, and  becomes  acquainted  with  the  most  im- 
portant instruments  and  their  uses.  Thus  he  is  prepared 
to  listen  appreciatively  to  an  unvarnished  tale,  in  which 
are  set  forth  the  principal  things  which  are  known  or 
reasonably  surmised  concerning  the  worlds  around  us. 

The  effectiveness  of  the  presentation  of  the  subject  is 
much  enhanced  by  the  illustrations,  for  many  of  the 
finest  of  which  the  thanks  of  both  reader  and  author  are 
due  to  the  directors  of  the  Lick  and  Harvard  College 
Observatories,  and  to  the  editors  of  Popular  Astronomy, 
Knowledge,  and  The  Astrophysical  Journal. 

Notice  of  any  error  will  be  gratefully  received  by  the 
author,  whose  address  is  Chamberlin  Observatory,  Uni- 
versity Park,  Colorado. 


CONTENTS. 


CHAPTER 


I.     INTRODUCTION   AND    HISTORICAL 

SKETCH 15 

II.     THE   HEAVENS  AND   THEIR  APPARENT 

DAILY  REVOLUTION 36 

III.  THE  CONSTELLATIONS  IN  GENERAL    .      48 

IV.  THE    CONSTELLATIONS     FOR    JANUARY 

AND  FEBRUARY 56 

V.     THE  CONSTELLATIONS  FOR  MARCH  AND 

APRIL 79 

VI.     THE   CONSTELLATIONS   FOR   MAY  AND 

JUNE 95 

VII.     THE  ASTRONOMER *  .     m 

VIII.     A  GREAT  TELESCOPE 128 

IX.     THE   ASTRONOMER'S   WORKSHOP,  AND 

SOME  OF  His  TOOLS 143 

X.     TIME 167 

XL     THE   SUN 179 

XII.     THE    MOON   AND    ECLIPSES 205 

XIII.  MERCURY   AND    VENUS   .......    231 

XIV.  MARS  AND  THE  ASTEROIDS 236 

XV.     JUPITER,  SATURN,  URANUS,   AND  NEP- 
TUNE   253 

XVI.     COMETS  AND  METEORS 271 

XVII.     THE  FIXED  STARS 301 

XVIII.     THE  NEBULAE    ........    .    .    .    321 


DIAGRAMS  AND  ILLUSTRATIONS. 

The  Moon  Partially  Eclipsed Frontispiece. 

FIGURE  PAGE 

1.  The  Moon 19 

2.  Cycle  and  Epicycle 25 

3.  Tycho 28 

4.  Kepler 30 

5.  Galileo 31 

6.  Sir  Isaac  Newton 33 

7.  Laplace 34 

8.  A  Section  of  the  Milky  Way .  37 

9.  The  Great  Dipper 40 

10.  Measurement  of  an  Angle 41 

11.  The  Two  Dippers 45 

12.  Ursa  Major 59 

13.  Ursa  Minor 61 

14.  Cassiopeia 63 

15.  Pegasus 65 

16.  Aquarius 66 

17.  Pisces 68 

18.  Andromeda 70 

19.  Aries 71 

20.  Cetus 71 

21.  Taurus 73 

22.  Orion 75 

23.  Auriga 77 

24.  Gemini 80 

25.  Perseus 82 

26.  Cancer 83 

27.  Canis  Major 84 

28.  Canis  Minor 85 

29.  Lepus 85 

30.  Leo 86 

31.  Bootes ;......'.  \   .  88 

32.  Virgo 90 

ix 


Diagrams  and  Illustrations. 


33.  Corvus 91 

34.  Corona  Borealis 92 

35.  Hydra 93 

36.  Lyra 95 

37.  Hercules   .    .    .    : 97 

38.  Cygnus 98 

39.  Draco 100 

40.  Sagitta 101 

41.  Scorpio 102 

42.  Libra 103 

43.  Delphinus     104 

44.  Aquila 105 

45.  Serpens  and  Ophiuchus .......  106 

46.  Sagittarius 108 

47.  Cepheus 109 

48.  Capricornus no 

49.  Charles  A.  Young 112 

50.  Edward  S.  Holden ;  .    .  114 

51.  Simon  Newcomb 115 

52.  Benjamin  A.  Gould 116 

53.  Edward  C.  Pickering 117 

54.  William  H.  Pickering 119 

55.  Edward  E.  Barnard 120 

56.  James  E.  Keeler 121 

57.  First  Position  of  the  Spider-webs 123 

58.  Second  Position  of  the  Spider-webs 123 

59.  A  Micrometer 124 

60.  Third  Position  of  the  Spider-webs 124 

61.  Seth  C.  Chandler 125 

62.  Sherburne  W.  Burnham 126 

63.  The  Yerkes  Telescope  at  the  Columbian  Exposition  .  129 

64.  Alvan  G.  Clark 130 

65.  Lump  of  Optical  Glass 132 

66.  The  Lump  Cut  Down 133 

67.  The  Lump  Molded 133 

68.  The  Lump  after  Further  Cutting 134 

69.  The  Lump  Cut  Down  Still  More 134 

70.  Machine  for  Polishing  Lenses 135 

71.  Alvan  Clark's  Workshop 136 

72.  John  A.   Brashear 137 


Diagrams  and  Illustrations.  xi 


73.  The  Two  Lenses  of  an  Object-Glass 138 

74.  An  Equatorial  Telescope 139 

75.  The  Chamberlin  Telescope  of  the  University  of  Den- 

ver   , 141 

76.  The  Yerkes  Observatory 144 

77.  The  Chamberlin  Observatory 145 

78.  Main  Floor  of  the  Chamberlin  Observatory 147 

79.  A  Meridian  Circle 150 

80.  The  Spider-webs 152 

81.  The  Spire  on  the  Cross  Wires 153 

82.  The  Lick  Observatory 155 

83.  A  Chronograph 157 

84.  A  Portion  of  a  Chronograph  Sheet  .       158 

85.  The  Lick  Micrometer 159 

86.  Measurement  of  a  Planet's  Diameter 160 

87.  Bisection  by  Spider-webs 161 

88.  Essentials  of  a  Spectroscope 162 

89.  A  Spectroscope 165 

90.  A  Watch  Balance 177 

91.  Sun-spots 183 

92.  Changes  in  a  Solar  Spot 184 

93.  A  Portion  of  the  Photosphere 187 

94.  Faculcs 190 

95.  Prominences 191 

96.  A  Quiescent  Prominence 192 

97.  The  Corona  of  July,  1878 194 

98.  The  Corona  of  January,  1889 195 

99.  The  Corona  of  April,  1893 196 

100.  Lunar  Formations 207 

101.  Lunar  Plains,  called  Seas 210 

102.  Copernicus 213 

103.  The  Apennines 216 

104.  The  Mare  Crisium 219 

105.  A  Rugged  Region  near  Tycho 223 

106.  Moon's  Shadow  on  the  Earth,  as  seen  from  the  Moon,  227 

107.  Conjunction  and  Elongation 232 

108.  Markings  on  Venus 235 

109.  Mars 236 

no.  Projections  on  the  Polar  Cap 238 

in.  The  Lake  of  the  Sun 239 


xii  Diagrams  and  Illustrations. 


FIGURE  PAGE 

112.  Canals • 241 

113.  Projections  on  the  Edge  of  the  Disc 242 

114.  Canals  connected  with  Lacus  Solis 243 

115.  The  Polar  Cap  in  July  and  August,  1892 244 

116.  Canals  in  August,  1892 245 

117.  The  Cap  Diminishing,  August  24-9,  1892 246 

118.  Asteroid  Trail  on  a  Photograph  of  the  Pleiades  ...  249 

119.  Jupiter 254 

120.  The  Great  Red  Spot 256 

121.  Saturn 261 

122.  Sir  William  Herschel 266 

123.  Discovery  of  a  Comet  by  Photography 272 

124.  Paths  of  Comets 273 

125.  Jets  and  Envelopes 276 

126.  Photographs  of  Swift's  Bright  Comet  of  1892  ....  279 

127.  Holmes's   Comet 282 

128.  Photograph  of  Rordame's   Comet,  showing  Masses 

of  Matter  driven  off  into  the  Tail 285 

129.  Comet  c,  1893  (Brooks) 287 

130.  A  Besprinkling 290 

131.  Photograph    showing  a  Meteor's    Path    among    the 

Stars      293 

132.  A  Meteorite  seen  July  27,  1894 298 

133.  Outlines  of  Dark  Structures  in  the  Galaxy 302 

134.  A  Part  of  the  Milky  Way  in  Cygnus 304 

135.  Motion  of  the  Components  of  a  Double  Star  ....  308 

136.  A  Rich  Portion  of  the  Milky  Way 312 

137.  The  Great  Globular  Cluster  in  Hercules 315 

138.  Cloudy  Region  in  the  Milky  Way 318 

139.  A  Spiral  Nebula 322 

140.  The    Nebula    of  Orion    Photographed.       Exposure, 

fifteen  minutes 324 

141.  The  Nebula  of  Orion  Photographed.     Exposure,  two 

hours 324 

142.  The  Nebula  of  Orion  Photographed.     Exposure,  nine 

hours     325 

143.  A  Drawing  of  the  Central  Part  of  the  Great  Nebula 

in  Orion 329 

144.  The  Ring  Nebula  in  Lyra 334 


C.   L.  S.   C.   MOTTOES. 

WE  STUDY  THE  WORDS  AND  THE  WORKS 
OF  GOD. 

LET  us  KEEP  OUR  HEAVENLY  FATHER  IN 

THE  MIDST. 

NEVER  BE  DISCOURAGED. 
LOOK  UP  AND  LIFT  UP. 


A   STUDY    OF   THE   SKY. 
CHAPTER  I. 

INTRODUCTION    AND    HISTORICAL    SKETCH. 

"  The  heavens  declare  the  glory  of  God  : 
And  the  firmament  sheweth  his  handy  work." 

THE  starry  spheres  which  roll  and  shine,  uncounted 
millions,  in  the  infinite  depths  of  space  call  us  away  Thestarr 
from  the  common  things  of  earth,  and  bid  us  plume  our  sPheres- 
spirits  for  the  loftiest  flights.  Not  in  the  garish  glory  of 
the  day,  when  men's  eyes  are  well-nigh  blinded  by  the 
affluence  of  light  which  the  sun  pours  forth,  and  their 
minds  are  caged  in  the  narrow  round  of  daily  toil,  are 
the  wonders  of  the  sky  revealed.  But  when  the  clangor 
and  roar  of  the  world' s  traffic  have  died  away,  and  the 
last  glint  of  the  retiring  sun  has  vanished  from  the 
mountain  top  ;  when  the  soft  shades  of  the  evening  twi- 
light gradually  melt  into  the  darkness  of  the  night,  and 
the  blessed  shadow  of  the  earth  steals  over  the  abodes  of  The  blessed 
men,  bringing  rest  and  refreshment  of  mind,  then  come 
forth  the  troops  of  radiant  orbs,  filling  the  sky  with  their 
splendid  array,  and  giving  to  the  mind  of  the  beholder 
a  portion  of  their  own  eternal  calm. 

"The  starry  skies,  they  rest  my  soul, 
Its  chains  of  care  unbind, 
And  with  the  dew  of  cooling  thoughts 
Refresh  my  sultry  mind. 

"  And  like  a  bird  amidst  the  boughs 
I  rest,  and  sing  and  rest, 
Among  those  bright  dissevered  worlds, 
As  safe  as  in  a  nest." 

15 


i6 


A  Study  of  the  Sky. 


Mysteries  are 
unraveled. 


Powerful 
instruments. 


With  this  calmness  of  mind  comes  reflection,  followed 
by  a  keen  thirst  for  knowledge.  The  enigma  of  the 
universe  is  thrust  upon  the  beholder,  and  he  accepts  the 
challenge  to  solve  it.  Year  after  year,  century  after 
century,  has  the  dauntless  mind  of  man  climbed  the 
arduous  steep  which  leads  to  a  knowledge  of  the  stars. 
Each  defeat  has  stimulated  it  to  greater  exertions  and 
more  glorious  victories.  Barrier  after  barrier  has  been 
surmounted  or  broken  down.  Difficulty  after  difficulty 
has  vanished  before  persistent  effort. 

Ingenious  and  powerful  instruments  have  been  de- 
vised, which  reveal  wonders  otherwise  unimagined,  and 
the  end  is  not  yet.  Each  new  telescopic  giant  is  ex- 
pected to  win  fresh  laurels  in  old  fields  of  endeavor,  or 
to  make  discoveries  which  shall  link  its  name  forever 
with  the  stars.  When  the  great  thirty-six-inch  glass, 
the  fame  of  which  has  spread  throughout  the  world,  was 
set  up  on  Mt.  Hamilton,  a  poet's  fancy  was  stirred,  and 
he  addressed  the  ensuing  lines  to  the  lens.* 

"  Perchance  that  thou 
With  cloudless  vision  slowly  sweeping  up 
The  mighty  Nave  that  cleaves  the  Galaxy — 
God's  visible  Tabernacle  in  the  skies, 
Star-built  from  shining  undercroft  to  dome, 
Past  pillared  pomp  of  worlds,  and  columns  wrought 
With  fair  entangle  of  amethyst  and  pearl, 
Thro' jacinth  portals  hung  with  mist  of  stars, 
And  fiery  fringe  of  suns — mayst  come  at  last 
Even  to  the  chancel  of  the  Universe  ; 
And  so  thro'  glories  veiled  and  far,  behold 
/The  Choral  Stars  that  sang  so  loud  and  sweet 
I  On  the  first  morning  when  creation  sprang 
l  In  dewy  beauty  from  Jehovah's  hand. 
Mayhap  that  thou,  with  swiftness  unconceived, 
Wilt  overtake  the  light  and  see  the  things 


*  "  Handbook  of  the  Lick  Observatory,"  page  76. 


Introduction  and  Historical  Sketch.  17 

That  have  been,  and  that  shall  be  nevermore  ; 
Follow  the  dying  star  in  her  swift  flight 
Athwart  Eternity  ;  track  the  lost  world, 
That  drifting  past  our  ken,  still  gleameth  fair 
Upon  the  confines  of  some  far-off  realm  ; 
Perchance  the  Star  which  first  spake  peace  to  men 
Will  dawn  through  thee  upon  the  waiting  earth  ; 
And  O  far-seeing  Eye,  perchance  mayst  thou 
Reveal  the  City  Beautiful  which  lies 
Four-square  in  midst  of  heaven,  whose  shining  walls 
Are  of  fair  jasper  builded  and  pure  gold  ; 
Whose  battlements  are  crystal  and  whose  ways 
Are  sapphire  paven,  and  whose  gates  are  pearl." 

No  astronomer  has  any  expectation  of  such  good  for- 
tune as  the  poet  has  outlined.     But  the  spacious  firma-   God  ™ajesty  of 
ment,  to  the  study  of  which  he  gives  his  nightly  vigils  revea 
and  his  daily  toils,  is  the  handiwork  of  the  Most  High, 
and    continually   reveals    to    the    earnest    student   the 
majesty  and  glory  of   the  omnipotent,  the    ever-living 
God. 

Many  and  toilsome  have  been  the  steps  by  which  the  The  iadder  of 
astronomers  of  centuries  past  and  present  have  mounted  Pro&ress- 
the  long  ladder  whose  base  rests  on  the  earth,  and  whose 
summit  is  now  to  be  found  among  the  star-clouds  of  the 
Milky  Way. 

The  first  astronomer  was  Adam  :  his  observatory  was 
one  of  the  flower-decked  mounds  of  the  Garden  of  Eden,  astronomer. 
His  two  telescopes  were  fresh  from  a  celestial  workshop. 
What  must  have  been  his  feelings  as  the  glowing  orb  of 
day,  which  had  warmed  his  body  and  cheered  his  spirit, 
sank  in  the  west  and  the  evening  twilight  deepened  ! 
Was  he  to  be  imprisoned  in  a  dungeon  of  darkness,  and 
the  beautiful  creation  about  him  to  fade  into  nothingness  ? 

Behold  !  a  new  light  appears  in  the  sky  ;  the  silvery 
moon,  which  has  been  appointed  to  rule  the  night, 
stands  out  in  all  her  beauty,  and  casts  dim  shadows  of 


i8 


A  Study  of  the  Sky. 


The  moon  and 
stars  appear. 


The  Milky 
Way. 


Adam  sleeps 
and  wakens. 


the  foliage  on  the  darkening  turf.  But  hers  is  not  the 
only  light.  Here  and  there,  scattered  over  the  broad 
expanse  of  the  sky,  appear  the  brighter  stars,  set  like 
jewels  as  a  crown  upon  earth's  brow.  They  have 
various  colors  and  degrees  of  brightness  :  a  multitude  of 
lesser  lights  gradually  come  forth,  forming  strange  con- 
figurations. Now,  for  the  first  time,  the  solitary  observer 
notices  that  the  moon  is  following  the  sun  to  a  grave 
in  the  west,  and  that  the  stars  too  are  joining  in  the  gen- 
eral movement.  Will  all  at  last  be  lost  to  his  vision, 
and  darkness  rule  supreme  ?  He  faces  eastward  and 
sees  new  groups  of  stars  rising  to  take  the  places  of 
those  which  are  passing  away.  The  moon  sinks  in  the 
west  ;  earnestly  he  watches  the  glow  on  the  horizon  at 
the  point  where  she  disappeared,  until  it  fades  away. 

Upward  again  he  throws  his  inquiring  glance,  and  be- 
holds the  most  wonderful  sight  of  all.  Athwart  the  star- 
sphere  a  broad  river  of  light  pursues  its  tortuous  way. 
In  places  it  glows  as  if  pent-up  fires  were  about  to  burst 
forth  ;  in  other  places  are  black  rifts,  which  seem  to  in- 
tensify the  darkness  of  the  night.  Upon  all  nature  has 
fallen  a  solemn  hush,  broken  only  by  the  faint  notes  of  a 
far-away  nightingale.  A  strange  drowsiness  creeps  over 
our  great  ancestor  and  fills  him  with  dread  :  in  vain  he 
fights  against  it  :  overcome  he  sinks  down  and  is  lost  in 
slumber.  What  visions  may  have  come  to  him  we  know 
not.  The  hours  roll  on,  and  the  stars  keep  silent  vigil 
over  the  slumberer  :  at  last  the  aurora  of  approaching 
day  glows  along  the  eastern  horizon.  He  awakens  and 
feels  the  pleasurable  glow  of  fresh  life  and  vigor.  The 
stars  fade  from  view,  and  the  first  glint  of  the  glad  sun- 
shine greets  his  vision.  The  sun  arises  in  its  full  glory, 
and  animate  nature  is  awakened.  The  man  wonders 
and  adores.  Surely  he  will  be  a  lover  of  nature  for  life. 


Introduction  and  Historical  Sketch. 


The  majestic  revolution  of  the  heavens,  the  waxing  and 
waning  of  the  moon,  the  movements  of  the  brilliant 
planets,  an  occasional  outburst  of  a  comet,  all  these  will 


FIG.  i.— THE  MOON. 


continually  delight   him,   and   will    ever   lead   to  fresh 
adoration  of  his  Creator. 

How  rudely  are  our  bright  expectations  of  Adam's  The  first  appii- 
astronomical  joys  shattered  !    For  a  rationalistic  instruc-   scientific 
tor  in  the  domain  of   theology,  the  wily  serpent,  took 


20 


A  Study  of  the  Sky, 


A  step  forward. 


The 
"Rigveda.' 


Josephus. 


Adam  and  his  companion  in  hand.  Under  his  tuition 
they  introduced  the  genuine  scientific  method  of  investi- 
gation, the  method  of  experiment  and  observation,  into 
fields  theological.  Inestimable  as  may  be  the  value  of 
this  method,  it  brought  ruin  and  desolation  to  the  first 
experimenters. 

Brought  sharply  to  his  senses  by  being  driven  from 
his  beautiful  dwelling  place,  forced  to  earn  his  subsist- 
ence by  the  sweat  of  his  brow,  burdened  with  increasing 
cares  and  sorrows,  Adam's  spirit  was  much  broken,  and, 
like  Bunyan's  man  with  a  muck-rake,  he  acquired  the 
habit  of  looking  downward  instead  of  upward. 

We  must  take  a  long  step  forward  to  find  the  first 
glimmerings,  more  or  less  historic,  of  the  lamp  of 
astronomical  knowledge.  We  thus  emerge  from  the 
realm  of  fancy  in  which  we  have  disported  ourselves  for 
a  time  into  the  dim  borderland,  in  which  history  and 
myth  are  interwoven,  and  we  shall  press  on  speedily 
into  the  full  light  of  historic  fact. 

Among  the  first  of  astronomical  allusions  are  those  con- 
tained in  the  writings  of  the  early  Aryans,  by  whom  the 
hymns  of  the  * '  Rigveda  "  were  written.  These  writings, 
however,  serve  only  to  reveal  to  us  primitive  notions 
about  the  earth  and  the  firmament,  and  do  not  contain 
astronomical  observations.  The  earth  is  represented  as 
a  flat  surface,  on  whose  broad  expanse  rests  the  blue 
and  ever-changing  vault  of  heaven.  Below  this  star- 
spangled  vault  is  the  home  of  the  life-giving  light. 

Josephus  states  that  one  reason  why  the  lives  of  the 
antediluvian  patriarchs  were  prolonged  was  that  they 
might  perfect  the  sciences  of  geometry  and  astronomy, 
which  they  had  discovered.  He  also  informs  us  that 
these  primitive  scientists  had  learned  from  Adam  that 
the  world  was  to  perish  by  water  and  by  fire  ;  fearing 


Introduction  and  Historical  Sketch.  21 

therefore  that  the  results  of  their  centuries  of  labor 
would  be  lost,  they  built  two  columns,  one  of  brick  and 
the  other  of  stone,  which  bore  inscriptions  intended  to 
preserve  the  knowledge  which  their  toil  had  wrested 
from  the  sky.  In  case  the  deluge  destroyed  the  brick 
column,  the  stone  one  at  least  would  come  through  un- 
harmed. Josephus  would  have  us  believe  that  the  stone 
monument  was  still  to  be  seen  in  his  day. 

Herodotus,  the  father  of  history,  makes  the  astonish-  Herodotus 
ing  statement  that  the  Egyptians  had  made  astronomical 
observations  for  11,340  years,  and  had  seen  the  earth's 
equator  perpendicular  to  the  plane  of  its  orbit.  But  the 
present  refinement  of  astronomical  theory  forbids  a  belief 
that  the  equator  and  ecliptic  have  been  perpendicular 
within  the  memory  of  man,  and  lends  no  countenance  to 
the  theory  that  they  ever  were. 

A    high    antiquity   is    claimed    for   the   beginning   of 
astronomy   among    the    Chinese.     Forty-five   centuries   Early  Chinese 

0  .    .  .  astronomy. 

ago  the  emperor  Hoang-Ti  is  reputed  to  have  built  an 
observatory,  and  to  have  appointed  an  astronomical 
board,  upon  the  members  of  which  devolved  the  duties 
of  regulating  the  times  of  the  religious  festivals.  The 
ancient  chronicles  also  relate  that  once  upon  a  time  the 
astronomical  board,  which  consisted  of  two  learned 
gentlemen  bearing  the  rather  hilarious  names  of  Hi  and 
Ho,  forgot  the  dignity  of  its  high  position,  and  indulged 
in  riotous  living.  Meanwhile  the  moon  stole  a  march 
on  the  board,  and  eclipsed  the  sun.  China  was  thus 
exposed  to  the  wrath  of  the  gods,  because  the  eclipse 
had  not  been  foreseen  and  the  proper  religious  rites 
observed.  The  emperor  at  once  accepted  the  resigna- 
tion of  the  board,  by  the  sword  of  the  executioner. 
The  Chinese  astronomical  records  of  the  past  twenty-six 
centuries  are  thought  to  be  fairly  reliable  ;  they  contain 


22 


A  Study  of  the  Sky. 


Babylonian 
astronomy. 


Grecian 
philosophers. 


Pythagoras. 


accounts  of  the  appearances  of  remarkable  comets,  as 
well  as  data  concerning  eclipses. 

We  must  look  to  the  plains  of  Babylonia  for  the  most 
valuable  early  observations.  The  mild  climate  and  open 
sky  of  Central  Asia  favored  the  development  of  the 
science  of  the  stars.  We  are  not  surprised,  then,  to 
find  that  the  Chaldeans  were  acute  and  patient  observers 
through  many  generations,  and  accumulated  a  very 
respectable  store  of  observational  knowledge.  Their 
greatest  achievement  lay  in  the  line  of  observations  of 
eclipses  of  the  sun  and  moon.  By  careful  study  of  the 
times  at  which  eclipses  had  happened,  they  discovered 
that  those  phenomena  repeated  themselves  in  cycles  of 
about  eighteen  years.  Thus  they  were  enabled  to  fore- 
tell eclipses  with  considerable  accuracy.  But  of  the 
real  causes  of  those  interesting  phenomena  they  were 
ignorant. 

To  the  ancient  Greeks  modern  astronomy  owes  a 
great  debt.  So  sublime  and  mysterious  are  the 
heavenly  bodies,  and  so  intricate  their  motions,  that 
the  speculative  minds  of  the  early  Grecian  philosophers 
were  irresistibly  attracted  to  a  study  of  them.  Though 
many  of  their  theories  were  groundless,  and  many  of 
their  statements  obscure  and  mingled  with  metaphysics 
in  a  most  curious  fashion,  yet  gems  of  truth  are  to  be 
found  here  and  there,  which  well  repay  the  labor  spent 
in  searching  them  out. 

Though  Plato  suggested  that  the  world  was  a  cube, 
which  seemed  to  him  the  most  perfect  of  solids, 
Eudoxus,  Archimedes,  and  Aristotle  made  it  a  sphere. 
Nicetas  is  said  to  have  ascribed  the  apparent  daily 
revolution  of  the  celestial  sphere  to  the  revolution  of  the 
earth  upon  its  axis. 

To  Pythagoras  is  attributed  the  beautiful  but  utterly 


Introduction  and  Historical  Sketch. 


erroneous  doctrine  of  the  crystalline  spheres.  I'n  the 
outermost  of  these  were  set  the  fixed  stars,  which  had, 
long  before  his  time,  been  grouped  in  constellations,  and 
associated  with  mythological  characters.  Each  planet 
too  had  its  sphere.  To  him  also  is  ascribed  the  theory 
that  the  sun  is  the  center  about  which  the  earth  and  the 
other  planets  move  ;  this  would  nowadays  be  called 
a  "  class-room  theory,"  because  it  was  not  promulgated 
except  in  a  private  way  among  his  students.  Philolaus,  \ 
a  follower  of  Pythagoras  and  a  contemporary  of  Socrates,  / 
taught  the  doctrine  openly.  j 

But  the  overwhelming  influence  of  Aristotle  soon  Aristotle> 
erased  it  from  the  Greek  mind.  He  placed  the  earth 
immovable  in  the  center  of  the  universe,  and  did  not 
allow  it  to  rotate  upon  its  axis.  The  celestial  bodies 
were  permitted  to  revolve  around  the  earth  in  decorous 
fashion.  So  powerful  was  the  influence  of  this  intellec- 
tual giant  upon  the  minds  of  thinking  men  for  centuries 
afterward,  that  the  earth  was  not  finally  and  forever  dis- 
placed from  the  erroneous  position  which  he  assigned  to 
it  till  the  days  of  Copernicus. 


To  the  second  century  before  Christ  belongs  Hippar- 
chus,  justly  called  the  father  of  astronomy,  who  rescued 
Greek  astronomy  in  large  measure  from  the  bog  of  spec- 
ulation into  which  earlier  philosophers  had  plunged  it, 
and  made  it  a  science  of  observation  as  well  as  of  theory. 
He  was  a  genius  of  the  highest  order,  being  at  once  an 
accurate  observer  of  the  celestial  bodies,  a  profound 
mathematician,  and  a  brilliant  theorist.  He  devised  the 
system  of  locating  places  on  the  earth  by  means  of  their 
latitude  and  longitude.  In  order  to  facilitate  his  compu- 
tations he  invented  that  branch  of  mathematics  now 
called  trigonometry.  The  first  catalogue  of  the  fixed 
stars  is  due  to  his  labors.  The  apparent  motions  of  the 


Hipparchus. 


A  Study  of  the  Sky. 


Ptolemy. 


The  shape  of 
the  earth. 


The  earth's 
place. 


sun  and  moon  he  explained  by  an  ingenious  theory, 
which  he  tested  by  observation  and  computation.  In 
determining  the  length  of  the  year  he  made  an  error  of 
only  four  minutes. 

After  Hipparchus  the  most  distinguished  astronomer 
J  of  antiquity  was  Ptolemy,  who  lived  at  Alexandria  in  the 
/  second  century  of  our  era,  and  wrote  the  "Almagest," 
which  has  come  down  to  us  entire,  and  in  which  is  pre- 
served nearly  all  our  knowledge  of  Greek  astronomy. 
As  the  Ptolemaic  system  was  the  orthodox  astronomy  of 
the  next  fourteen  centuries,  we  notice  a  few  of  its  chief 
principles. 

The  earth,  said  Ptolemy,  must  be  round.  For  if  one 
go  southward  new  stars  appear  above  the  southern  hori- 
zon, and  stars  in  the  north  seem  nearer  the  horizon  than 
before.  Besides  this,  the  heavenly  bodies  do  not  rise  at 
the  same  moment  for  two  observers,  one  of  whom  is  east 
of  the  other.  Furthermore,  when  a  sailor  approaches 
the  coast,  the  bases  of  the  headlands  are  at  first  hidden 
from  view  by  reason  of  the  curvature  of  the  sea. 
A  The  earth  must  also  be  in  the  center  of  the  celestial 
sphere,  for  if  it  were  nearer  to  the  eastern  portion  of  the 
heavens  than  to  the  western  the  stars  in  the  east  would 
seem  to  move  with  greater  rapidity  than  those  in  the 
west.  Since  the  stars  sweep  across  the  sky  each  day  at 
a  perfectly  regular  rate,  the  earth  must  be  equally  dis- 
tant from  all  of  them,  and  thus  in  the  center  of  the  uni- 
verse. 

What  is  the  shape  of  the  curve  in  which  every 
heavenly  body  moves?  Ptolemy  replies  that  it  is  a 
circle,  the  most  perfect  of  all  curves.  Now  an  objector 
might  say  that  this  would  do  for  the  fixed  stars,  the  sun, 
and  the  moon,  which  move  with  exceeding  regularity, 
but  how  could  it  explain  the  apparent  motion  of  Saturn, 


Introduction  and  Historical  Sketch. 


FIG.  2.— CYCLE  AND  EPICYCLE. 


or  of  Jupiter,  both  of  which  move  irregularly  ?      Here 
Ptolemy  had  recourse  to  the  device  of  the  epicycle,  in-   Cycles  and 
troduced  by  Hipparchus.     The  word  epicycle  is  derived 
from    two    Gre  ek 
words,      meaning 
"upon''     and    '  'a 
circle."     The  epicycle 
was  a  circle  the  center 
of  which  moved  along 
the    circumference    of 
another    circle.       The 
idea  is  easily  grasped 
by  reference  to  Fig.  2. 
E  represents  the  earth ; 
Jupiter,  located   at    J, 
moves      uniformly 
around  the  circumfer- 
ence of  the  small  circle,  while  P,  the  center  of  that  cir- 
cle, moves  along  the  circumference  of  the  large  circle. 

Ptolemy  found,  by  comparing  his  observations  with 
those  of  Hipparchus,  that  he  could  not  explain  the 
motions  of  the  sun,  moon,  and  planets  with  sufficient 
accuracy  by  so  simple  a  device.  But  by  adding  ad- 
ditional epicycles,  and  by  placing  the  earth  at  a  short 
distance  from  the  center  of  the  large  circle  in  the  dia- 
gram, he  could  explain  the  irregularities  which  per- 
plexed him. 

After  Ptolemy's  death  the  study  of  astronomy  grad- 
ually declined,  and  suffered  a  decided  set-back  in  the 
burning  of  the  great  library  at  Alexandria,  in  the  middle 
of  the  seventh  century.  To  the  Arabians,  who  now 
made  Bagdad  the  literary  center  of  the  civilized  world, 
we  must  look  for  the  next  advances.  They  were  assid- 
uous observers,  and  thus  furnished  a  groundwork  of  fact 


Arabian 
astronomy. 


26 


A  Study  of  the  Sky. 


upon  which  later  generations  might  build  theories,  and 
by  which  those  theories  might  be  tested. 

At  last  the  intellectual  aspirations  of  the  peoples  of 
T..h«  av?kenins  Western  Europe  were  awakened,  after  a  slumber  of  cen- 

ot  Western  _  x 

Europe.  turies.     The  lamp  of  learning,  which  was  burning  in  the 

Moorish  universities  of  Spain,  shed  its  beneficent  rays 
among  more  northern  nations.  The  Arabic  version  of 
Ptolemy' s  ' '  Almagest ' '  was  translated  into  the  Latin 
language  in  the  thirteenth  century,  under  the  patronage 
of  Frederick  II.,  emperor  of  the  Holy  Roman  Empire. 
In  the  same  century  Alphonso  X.,  king  of  Leon  and 
Castile,  who  was  surnamed  "The  Wise"  and  also 
' '  The  Astronomer, ' '  published  the  celebrated  Alphon- 
sine  tables,  which  were  prepared  with  immense  labor 
by  the  best  mathematicians  of  the  Moorish  universities. 
Observations  were  at  this  time  so  much  more  accurate 
and  numerous  than  in  the  days  of  Ptolemy  that  many 
epicycles  had  to  be  added  to  the  original  system,  in 
order  to  make  theory  correspond  with  observation.  The 
entire  heavens  were  said  to  be 

"  Scribbled  o'er 
With  cycle  upon  epicycle,  orb  on  orb." 


Alphonso's 
remark. 


Copernicus. 


So  complicated  had  the  celestial  machinery  become 
that  Alphonso  is  said  to  have  told  a  notable  gathering 
of  bishops  that  if  the  Almighty  had  done  him  the  honor 
to  consult  him  concerning  the  mechanism  of  the  uni- 
verse, he  could  have  offered  some  good  advice.  This 
irreverent  remark  may  have  been  inspired  by  the  de- 
pleted condition  of  the  royal  purse  after  the  publication 
of  the  tables. 

Three  centuries  had  yet  to  roll  away  before  deliver- 
ance from  the  thraldom  of  Ptolemy  came.  On  February 
12,  1473,  Nicholas  Copernicus  was  born  at  Thorn  in 


Introduction  and  Historical  Sketch.  27 

Prussia.  During  thirty-six  of  the  seventy  years  that 
were  allotted  to  him  he  studied  the  motions  of  the 
planets.  Throughout  a  large  part  of  his  life  he  held 
high  ecclesiastical  rank  as  canon  of  Warmia,  and  had 
leisure  for  his  favorite  investigations.  The  variations  in 
the  brightness  of  Mars  in  different  parts  of  its  orbit  were 
so  great  as  to  lead  him  to  think  that  the  earth  could  not 
be  the  center  about  which  Mars  revolved.  The  results 
of  his  meditations  are  set  forth  in  the  following  transla- 
tion of  his  own  words  : 

And  I  too,  on  account  of  these  testimonies,  began  to  meditate 
upon  the  movement  of  the  earth,  and  though  that  theory  seemed 
absurd,  I  thought  that  as  others  before  my  day  had  devised 
a  system  of  circles  to  account  for  the  motion  of  the  stars,  I  also 
might  endeavor,  by  supposing  that  the  earth  moved,  to  find  a 
more  satisfactory  scheme  of  the  movements  of  the  heavenly 
bodies  than  that  which  now  contents  us.  After  long  research  I 
have  become  convinced  that  if  we  assume  the  revolution  of  the 
earth  to  be  the  cause  of  the  wanderings  of  the  other  planets, 
observation  and  calculation  will  be  in  better  agreement.  And 
I  doubt  not  that  mathematicians  will  be  of  my  opinion,  if  they 
will  take  pains  to  examine  carefully  and  thoroughly  the  demon- 
strations to  be  given  in  this  book. 

Copernicus  broke  with  the  Ptolemaic  theory  at  two 

T  T        i          1     i  ,  r    1          1  The  new  vs.  the 

points.  He  placed  the  sun  in  the  center  of  the  planetary  id. 
system,  and  explained  the  diurnal  rotation  of  the 
heavens  by  the  revolution  of  the  earth  on  its  axis.  For 
a  long  time  he  hesitated  about  publishing  the  new  doc- 
trines, knowing  that  they  would  at  once  make  him 
a  target  for  the  ridicule  and  abuse  of  the  unthinking  and 
of  the  narrow-minded. 

The  insistence  of  his  warmest  friends,  particularly  of 

J  His  work  is 

the  bishop  of  Culm,  finally  led  to  the  publication  of  his  published, 
great  work,   which   was   entitled    "De    Revolutionibus 
Orbium  Ccelestium."      It  may  well  be  called  the  Magna 


28 


A  Study  of  the  Sky. 


its  importance.  Charta  of  astronomical  science.  Copernicus  did  not  live 
to  see  the  reception  which  was  accorded  it  ;  the  first 
copy,  fresh  from  the  press,  was  placed  in  his  hand  only 
a  few  hours  before  his  death.  In  one  important  particu- 
lar Copernicus  failed  to  break  with  Ptolemy  ;  he  still  re- 
tained the  system  of  epicycles,  but  the  innovations 

which  he  introduced 
simplified  it  greatly. 
The  new  system 
was  soon  to  be  put 
to  a  much  more 
searching  test  than 
Ptolemy's  had  been 
subjected  to.  In 
1546,  three  years 
after  the  death  of 
Copernicus,  there 
came  into  the  family 
of  a  Danish  noble- 
man a  son,  who 
afterward  became 
the  famous  Tycho 
Brahe.  In  those 
days  it  was  little 

short  of  a  misdemeanor  for  a  member  of  an  aristocratic 
family  to  engage  in  scientific  researches  ;  to  hunt  ani- 
mals and  to  kill  men  according  to  the  canons  of  war 
were  the  proper  pursuits.  The  young  noble  was  there- 
fore destined  for  the  army. 

When  but  fourteen  years  of  age  Tycho' s  curiosity  was 
aroused  by  the  occurrence  of  an  eclipse.  From  that 
time  forth  his  mind  was  with  the  stars.  Sent  to  Leipzig 
to  study  law,  he  could  not  be  induced  to  devote  himself 
to  it  ;  his  money  was  spent  for  astronomical  books  and 


Tycho  Brahe. 


An  eclipse. 


FIG.  3.— TYCHO. 


Introduction  and  Historical  Sketch.  29 

instruments,  and  his  time  was  largely  engrossed  with 
observations  of  the  stars.  In  1563  he  observed  a  con- 
junction of  Jupiter  and  Saturn,  which  he  thought  to  be 
the  cause  of  the  Great  Plague.  As  the  Gopernican 
tables  did  not  give  the  time  of  the  conjunction  accurately 
he  resolved  to  make  new  ones.  He  constructed  instru- 
ments of  large  size,  and  began  to  observe  with  fresh 
vigor.  The  king  heard  of  his  doings,  and  offered  him  a 
site  for  an  observatory,  ^20,000  for  the  building,  and 
a  life  pension  of  ^400.  The  observatory,  which  was 
called  Uranienburg  (the  Castle  of  the  Heavens),  was  uranienburg. 
erected  on  the  island  of  Huen,  near  Copenhagen.  It 
was  stocked  with  the  largest  and  finest  instruments 
which  the  mechanics  of  that  day  could  build.  For 
twenty  years  he  worked  with  the  utmost  ardor,  accumu- 
lating a  vast  store  of  observations  of  far  greater  accuracy 
than  any  which  had  been  made  previously.  Of  the 
subsequent  death  of  his  patron,  his  own  impoverishment 
and  virtual  banishment,  we  may  not  give  the  details. 
On  October  24,  1601,  he  died,  after  a  painful  illness, 
during  which  he  frequently  called  out,  ' '  Ne  frustra 
vixisse  videar"  (May  I  not  seem  to  have  lived  in  vain!). 

Two  years  before  Tycho's  death,  Johann  Kepler  Kepler, 
became  his  pupil.  Tycho  was  one  of  the  greatest  of 
observers,  but  his  pupil  was  preeminent  as  a  theorist. 
Taking  up  Tycho's  observations  of  Mars  he  endeavored 
to  discover  the  laws  of  the  planet's  movement.  Hy- 
pothesis after  hypothesis  was  tried  and  rejected  ;  at  one 
moment  he  was  at  the  summit  of  hope  ;  at  another  he 
was  in  the  depths  of  disheartenment.  Struggling  with 
indomitable  perseverance  against  sickness,  poverty,  and 
misfortune,  harassed  by  domestic  troubles,  and  hampered 
at  every  turn,  he  pressed  on  through  weary  years  to 
final  victory. 


A  Study  of  the  Sky. 


Kepler's  laws. 


His  exultation. 


Three  laws  came  to  light  through  his  labors  : 
Law  \      Eacn  planet  moves  in  an  ellipse,  at  one  focus 

of   which    is   the 
sun. 

Law 
line 

planet  to  the  sun 
sweeps  over  equal 
areas  in 
times. 
Law  III. 


IS 

II.     The 
joining  a 


equal 


Galileo. 


The 

squares  of  the 
times  of  revolu- 
tion of  any  two 
planets  are  to 
each  other  as  the 
cubes  of  their 
mean  distances 
from  the  sun. 

Upon  the  dis- 
FIG.  4.— KEPLER.  covery  of    the 

third  law  his  exultation  knew  no  bounds,  as  the  follow- 
ing exclamation  shows  : 

Nothing  holds  me  :  I  will  indulge  in  my  sacred  fury  :  I  will 
triumph  over  mankind  by  the  honest  confession  that  I  have 
stolen  the  golden  vases  of  the  Egyptians  to  build  up  a  taber- 
nacle for  my  God  far  away  from  the  confines  of  Egypt.  If  you 
forgive  me,  I  rejoice  :  if  you  are  angry,  I  can  bear  it :  the  die 
is  cast,  the  book  is  written,  to  be  read  either  now  or  by  poster- 
ity, I  care  not  which  :  it  may  well  wait  a  century  for  a  reader, 
as  God  has  waited  six  thousand  years  for  an  observer. 

While  Kepler  was  making  his  immortal  studies  in 
theoretical  astronomy,  the  science  of  observation  took  a 
tremendous  stride.  Galileo,  then  a  professor  in  the 
University  of  Padua,  heard  that  a  Dutch  spectacle-maker 


Introduction  and  Historical  Sketch. 


had  found  a  combination  of  glasses  through  which  the  \ 
weathercock  on  the  church  spire  looked  larger.  Being 
familiar  with  the  laws  of  optics  he  began  to  ponder  over 
the  matter.  All  night  long  he  sat  in  a  brown  study  ;  by 
morning  the  solution  came,  and  he  soon  had  an  old 
organ  pipe  with  a  glass  at  each  end,  which  was  the  fore- 
runner of  the  great  telescopes  of  our  day.  The  Senate 
doubled  his  salary,  and  he  went  at  telescope-making  in 
earnest  ;  having  completed  one  which  magnified  thirty 
times  he  began  to  explore  the  heavens. 

The  moon  displayed  to  him  the  rocky  ramparts  and   Discoveries, 
battlemented  crags  of  her  mountains.     The  Milky  Way 
was  resolved  into  countless  stars  ; 

"Infinity's  illimitable  fields, 
Where  bloom  the  worlds  like  flowers  about  God's  feet." 

Jupiter  was  found  to  be  attended  by  four  moons,  the  en- 
tire system  being  a  miniature  of  the  solar  system.  The 
motions  of  these 
bodies  powerfully 
confirmed  the  the- 
ories of  Coperni- 
cus. The  surface 
of  the  sun  was  seen 
to  be  marred  by 
spots.  Venus  be- 
came a  waxing  and 
waning  crescent. 

The  Aristoteli- 
ans were  con- 
founded again  and 
again.  But  they 
had  their  revenge  upon  this  pestilent  fellow,  who  was 
turning  the  world  of  natural  philosophy  upside  down. 
The  hand  of  the  Inquisition  was  laid  upon  him.  But  inquisition. 


FIG.  5.— GALILEO. 


A  Study  of  the  Sky. 


Truth 
triumphant. 


Isaac  Newton.  \ 


why  relate  the  painful  tale  of  the  rigorous  examinations, 
and  the  recantation  finally  forced  upon  the  feeble  old 
man?  In  the  year  1642  the  shattered  body  of  the 
philosopher  was  laid  to  rest,  but  in  unconsecrated 
ground,  for  the  iron  heel  of  the  Inquisition  must  even 
grind  his  bones  !  Many  of  his  manuscripts  were  de- 
stroyed, and  his  friends  were  not  permitted  to  raise  a 
monument  in  his  honor. 

)*     But  the  truth,  which  had  thus  been  ruthlessly  trampled 
/  under  foot,  beneath  the  blue  skies  of  fair  Italy,  rose  in 
adamantine  strength  amid  the  sturdy  oaks  of  old  Eng- 
land.    On  Christmas  Day  of  the  year  in  which  Galileo 
died  there  was  born  a  boy  who  was  to  supplement  the 
j  work  not  only  of  Galileo,  but  also  of  Copernicus,  Tycho, 
/  and  Kepler,  and  to  be  recognized  as  the  master  mind 
among  the  world's  philosophers. 

Isaac  Newton  was  not  a  very  promising  lad,  until  the 
day  when  a  bigger  boy  conferred  a  signal  blessing  on 
the  world  by  kicking  him.  Young  Isaac  retorted  by 
thrashing  his  assailant,  and  then  proceeded  to  show  the 
rest  of  the  boys  at  school  that  he  could  beat  them  in 
their  studies.  So  keen  became  his  interest  in  books 
that  he  was  sent  to  Trinity  College,  Cambridge,  where 
his  remarkable  aptitude  for  mathematics  displayed  itself. 
We  cannot  recount  all  the  marvelous  researches  to 
which  Newton's  genius  lent  itself.  The  discovery  which 
concerns  us  at  present  is  that  of  the  law  of  gravitation. 
Copernicus  had  proved  that  the  planets  revolved 
about  the  sun  as  a  center.  Tycho  had  observed  with 
all  assiduity,  and  Kepler,  by  discussing  these  observa- 
tions, had  discovered  the  three  laws  which  bear  his 
name.  Galileo  had  not  only  enlarged  astronomical 
knowledge  by  the  use  of  the  telescope,  but  had  pro- 
mulgated the  laws  of  motion  of  bodies  on  the  surface  of 


Introduction  and  Historical  Sketch. 


33 


the   earth.     These    laws    were    admirably    restated   by 

Newton,  and  are  now  called  Newton's  lawrs.     But  the  Newton's  laws. 

crowning  glory  of  his  achievements  is  the  proof  that  the 


FIG.  6.— SIR  ISAAC  NEWTON. 

same  force  which  pulls  the  apple  to  the  earth  controls 
the  motion  of  the  moon,  and  binds  the  planets  to  the 
sun.  This  force  is  not  constant  in  intensity,  but  varies 
inversely  as  the  square  of  the  distance.  Kepler's  laws 
have  been  proven  to  be  necessary  consequences  of  the 


34 


A  Study  of  the  Sky. 


Its  wide 
application. 


law  of  gravitation.  The  entire  mechanism  of  the  plane- 
tary movements,  not  their  elliptical  paths  alone,  but  also 
their  small  departures  from  true  ellipses,  caused  by  their 


FIG.  7. — LAPLACE. 

attractions   for  one  another,   are  all   explained  by  this 
simple  law. 

If  Newton's  law  be  correct,  will  not  the  mutual  attrac- 
tions of  the  planets  so  derange  their  orbits  that  at  last 


Introduction  and  Historical  Sketch.  35 

there  will  be  wreck  and  ruin,  where  now  are  order  and 
beauty  ?  During  the  last  century  Lagrange  and  La- 
place,  the  most  illustrious  of  French  mathematicians, 
proved  that  though  the  orbit  of  each  planet  alters  some- 
what, changing  in  both  shape  and  position,  the  disturb- 
ances are  confined  within  narrow  limits,  and  the  system 
of  planetary  worlds  is  therefore  stable. 

We  now  bring  our  rough  historical  outline  to  an  end, 
having  come  up  to  the  close  of  the  eighteenth  century, 
when  the  construction  of  large  telescopes  by  Sir  William 
Herschel  and  others  gave  a  special  impetus  to  observa- 
tional astronomy,  and  led  to  the  unfolding  of  the  science 
.along  new  lines. 


CHAPTER  II. 


The  arm-chair. 


Bright  stars. 


THE     HEAVENS    AND     THEIR    APPARENT     DAILY     REVO- 
LUTION. 

"  The  sad  and  solemn  night 
Has  yet  her  multitude  of  cheerful  fires  ; 
The  glorious  host  of  light 
Walk  the  dark  hemisphere  till  she  retires : 
All  through  her  silent  watches,  gliding  slow, 
Her  constellations  come,  and  climb  the  heavens,  and  go." 

PERMIT  the  author  to  talk  to  you,  the  reader,  for  a 
moment.  Perchance  you  are  seated  in  an  arm-chair, 
with  your  feet  on  the  fender,  and  this  book  in  your 
hands.  You  have  vanquished  Chapter  I.  and  are  ready 
for  fresh  victories.  The  next  foe  to  be  overcome  is  the 
arm-chair.  For  you  will  never  take  a  deep  interest  in 
astronomy  if  you  confine  yourself  to  an  arm-chair  and  a 
book.  A  young  man  rarely  becomes  enamored  of  a 
young  lady  into  whose  face  he  has  never  gazed.  You 
must  look  into  the  eyes  of  the  goddess  Urania  ;  they 
spangle  the  heavens,  and  will  well  repay  your  most 
ardent  gazing.  Surely  you  know  the  Great  Dipper, 
which  performs  the  endless  round  of  motion  about  the 
north  pole  of  the  sky.  But  are  you  acquainted  with 
Vega  the  beautiful,  Arcturus  the  magnificent,  Capella 
the  icy,  and  Sirius  the  glowing  ?  Why  do  we  call  Vega 
beautiful?  When  you  have  observed  its  hue,  you  will 
know.  Why  is  Arcturus  magnificent  ?  If  you  shall  be 
led  to  think  that  it  is  thousands  of  times  as  large  as  our 
sun,  you  will  not  begrudge  it  the  adjective.  In  the  dead 

36 


The  Heavens  and  their  Apparent  Revolution.       37 


Nebulae  and 
clusters. 


of  winter  look  up  through  the  frosty  air  at  Capella,  as  it 
stands   at  the  apex   of  the  starry  vault,  shining  with  a 
clear  white  light.      You  will  be  ready  to  admit  that  it  is 
a  fit  jewel  for  the  crown  of  the  ice-king.     As  soon  as 
your  own  eyes  have  marked  the  fact  that  Sirius  is,  in 
point  of  brightness,  a  seven-fold  Vega,  its  splendid  scin- 
tillations  will 
glow    in    your 
memory. 

Have  you  seen 
that  storehouse 
of  uncreated 
worlds,  the 
great  nebula  in 
Andromeda? 
Have  you  at 
any  time  turned 
your  opera- 
glass  upon  the 
famous  double 
cluster  in  Per- 
seus, or  upon 
the  Pleiades? 
How  many  stars 
can  you  see 
within  the  bowl 
of  the  Great 
Dipper?  Is 
your  eye  sufficiently  keen  to  split  the  double-star  Ep- 
silon  Lyrae,  which  lies  but  three  moon-breadths  from 
Vega  ?  Has  a  telescope  ever  split  again  each  of  these 
stars  for  you,  so  that  you  realized  that  they  formed  a 
svstem  of  four  revolving  suns  ?  Have  you  seen  Venus 

...  .  Venus  and  the 

at  mid-day,  or  can  you  recognize  her  in  the  evening,  as   moon. 


FIG.  8. — A  SECTION  OF  THE  MILKY  WAY. 


A  Study  of  the  Sky. 


The  Milky 
Way. 


Urania. 


The  fixed  stars. 


she  glows  with  silvery  sheen  in  the  west,  and  weaves  her 
way  in  and  out  among  the  stars,  from  night  to  night  ? 
Can  Venus  be  seen  at  midnight  ?  Is  the  full  moon  vis- 
ible at  noon  ?  Do  the  horns  of  the  crescent  moon  point 
toward  the  sun  ?  Does  the  moon  always  set  directly  in 
the  west  ?  In  what  direction  does  the  moon  move 
among  the  stars,  eastward  or  westward  ? 

On  some  night  when  the  sky  was  perfectly  clear,  and 
the  moon  was  not  in  sight,  have  you  made  a  study  of 
the  wonderful  river  of  light  which  foams  across  the  sky  ? 
Have  you  seen  the  dark  rocks  against  which  it  dashes, 
the  foaming  eddies  here  and  there,  and  the  profusion  of 
starry  spray  with  which  it  besprinkles  the  adjoining  con- 
stellations ? 

Must  you  give  a  negative  answer  to  most  of  these 
questions  ?  Then  let  the  arm-chair  control  you  no 
longer.  Yield  to  the  charms  of  Urania  :  woo  her,  and 
make  her  your  friend.  How  shall  this  wooing  proceed  ? 
This  chapter  and  the  next  four  shall  be  your  guide  in 
this  matter.  In  them  will  be  developed  an  orderly 
method  of  procedure,  which  will  lead,  by  easy  stages, 
to  the  attainment  of  the  desired  end. 

First  we  mention  briefly  the  classes  of  objects  with 
which  our  study  will  be  concerned. 

The  fixed  stars,  or  more  simply  the  stars,  are  those 
brilliant  points  of  light  which  stud  the  heavens,  remain- 
ing in  the  same  relative  position  from  year  to  year,  and 
from  century  to  century,  as  nearly  as  the  unaided  eye 
can  judge.  Had  an  ancient  Assyrian  made  a  rude  rep- 
resentation of  the  Great  Dipper  on  one  of  his  tablets  of 
clay,  we  should  at  this  day  instantly  recognize  the  con- 
figuration as  one  with  which  we  are  familiar.  The  fixed 
stars  are  suns,  at  such  amazing  distances  from  us  that 
their  motions  seem  exceedingly  small. 


The  Heavens  and  their  Apparent  Revolution.      39 

The  nebulae  are  cloud-like  masses  of  matter  of  vast 
extent,  which  are  as  far  away  as  the  stars.  The  great  The  nebulse- 
nebula  in  Andromeda  can  be  seen  easily  with  the  naked 
eye,  and  the  nebula  in  the  sword-handle  of  Orion  can  be 
glimpsed.  The  vast  majority  of  these  objects,  however, 
are  visible  only  with  powerful  telescopes.  Quite  a  num- 
ber are  invisible  even  in  the  largest  instruments,  but 
have  imprinted  themselves  on  photographic  plates  ex- 
posed for  hours  in  the  foci  of  special  star-cameras. 

The  planets  look  like  the  fixed  stars,  when  viewed 
with  the  naked  eye,  except  that  they  do  not  twinkle. 
Jupiter  and  Venus  are  usually  brighter  than  the  brightest 
fixed  stars.     Mars,  Mercury,  Saturn,  Uranus,  and  Nep- 
tune are  less  brilliant,  Neptune  never  being  visible  to 
the  unaided  eye.     The  ancients,  who  were  unacquainted  i 
with  Uranus  and   Neptune,    discovered  that  the  other 
planets   changed  their   apparent   positions    among   the 
stars.      From  this  circumstance  arose  the  designation 
"planet,"  which  signifies   "wanderer."     These  bodies 
are  all  comparatively  near  us,  the  most  distant  being  less 
than  three  thousand  million  miles  away.      The  minor  \ 
planets,  also  called  asteroids,  are  small  bodies  coursing  \ 
about  the  sun  in  paths  which  lie  between  those  of  Mars  j 
and  Jupiter. 

Comets    derive    their    name,    which    means    ' '  hairv   ,. 

Comets. 

ones,"  from  their  tails  or  trains,  which  often  attain  to 
great  magnificence.  Some  of  them  are  to  be  regarded 
as  members  of  the  solar  system,  since  they  revolve  about 
the  sun  in  closed  curves.  Others  are  simply  visitors, 
which  display  their  beauty  for  a  time,  and  then  whisk 
off  to  regions  unknown. 

Meteors  are  those  rash  little  bodies  which  plunge 
headlong  into  the  earth,  and  thus  end  their  careers  in  an 
outburst  of  evanescent  glory. 


A  Study  of  the  Sky. 


The  sun,  moon,  and  earth  need  no  particular  mention, 

Sun,  moon,  and   the  earth  being  one  of  the  sun's  family  of  planets,  and 

)  the  moon  being  her  attendant  ;  the  moon  belongs  to  the 

I  class    of    bodies    known    as    satellites,    which    revolve 

(  about  the  planets. 

We  are  now  in  a  position  to  understand  any  mention 
Ocr- 


The  Great 
Dipper. 


FIG.  9. — THE  GREAT  DIPPER. 

which  may  be  made  of  these  celestial  objects,  prior  to 
the  detailed  discussion  of  them  which  will  come  later. 

Our  present  business  is  to  get  acquainted  with  the  fixed 
stars.  The  Great  Dipper  is  the  first  configuration  to  be 
learned  (Fig.  9).  Around  the  margin  of  the  diagram  are 
given  dates,  which  will  aid  in  finding  it.  To  locate  it  on 
February  i  at  8  p.  m. ,  the  book  is  to  be  held  out  in  front 


The  Heavens  and  their  Apparent  Revolution.     41 


of  the  reader,  with  the  center  of  the  diagram  on  a  level 

with  his  eyes,  and  the  point  marked  February   i  at  the 

uppermost  part  of  the  circle.     The  diagram  then  shows 

that  the  Dipper  is  at  the  right  of  Polaris,  the  pole-star. 

Two  of  the  stars  in  the  bowl  are  called  the    Pointers, 

because    they    point    toward     Polaris.       The    distance 

between  the  Pointers  is  about  five  degrees,  and  should 

be  fixed  in  mind  as  a  sort  of  yardstick  with  which  to  The  yardstick. 

estimate  distances   between  other  stars.     The  distance 

from  Polaris  to  the  nearest  Pointer  is  about  five  times 

our  yardstick. 

In  order  to  get  an  accurate  notion  of  measurement  by 
degrees,  imagine  that  the  stars  are  fastened  upon  the  mefsurement. 
inner  surface  of  a  huge 
celestial  sphere,  the 
distance  from  the  earth 
to  the  surface  of  the 
sphere  being  so  great 
as  to  be  beyond  ade- 
quate comprehension 
(Fig.  10).  Let  E  be 
the  position  of  the  ob- 
server on  the  earth, 
while  S  and  S'  are  two 
stars  said  to  be  30° 
apart.  Through  these 

stars  a  circle  whose  center  is  at  E  is  drawn  on  the  sur- 
face of  the  celestial  sphere.  From  E  two  lines,  ES 
and  ES',  are  drawn,  making  the  angle  SES'.  This 
angle  is  measured  by  the  number  of  degrees  in  the  arc 
SS',  there  being  360°  in  an  entire  circle.  If  the  arc 
SS'  is  one  twelfth  of  the  entire  circumference,  the  angle 
SES'  is  an  angle  of  30°. 

Now  the  diameter  of  the  earth,   which  is  less  than 


FIG.  io.— MEASUREMENT  OF  AN  ANGLE. 


A  Study  of  the  Sky. 


Center  of  the 
sphere. 


8,000  miles,  is  very  minute  in  comparison  with  the 
distance  from  the  earth  to  any  fixed  star,  for  the  latter 
distance  is  expressed  by  many  millions  of  millions  of 
miles.  In  consequence  of  this,  the  angular  distance 
between. any  two  stars  always  appears  the  same,  wher- 
ever the  observer  may  be  on  our  planet. 

If   an    astronomer   in    Boston    were  to    measure  the 
Boston  and  San  angular  distance  between  Polaris  and  one  of  the  Pointers, 

Francisco.  . 

with  the  most  perfect  instrument  ever  devised  for  such 
work,  and  another  astronomer  in  San  Francisco  were  to 
make  a  similar  measurement,  the  two  results  would 
agree  if  the  observations  were  free  from  error.  This 
remark  applies  only  to  the  fixed  stars,  and  is  not  true 
of  the  moon  or  the  planets,  which  are  much  nearer  to  us. 

For  all  our  naked-eye  observations  we  may  therefore 
assume  that  the  eye  of  the  observer  is  located  in  the 
center  of  the  celestial  sphere,  and  that  all  of  the  fixed 
stars  are  fastened  to  the  sphere,  turning  with  it  as  it 
turns.  We  are  thus  taken  back  to  the  crystal  spheres, 
studded  with  golden  nails,  with  which  the  ancient 
Greeks  dealt.  We  may  imagine  the  moon,  the  planets, 
and  comets  to  be  likewise  located  on  the  inner  surface 
of  the  sphere,  but  to  be  endowed  with  powers  of  loco- 
motion, so  that  they  can  move  about  among  the  golden 
nails. 

Remembering  then  that  we  are  in  the  center  of  the 
celestial  sphere,  we  ask  the  question,  "How  does  the 
star-sphere  appear  to  turn?"  In  answering  this  we 
have  recourse  to  the  cause  of  the  apparent  turning, 
which  is  the  spinning  of  the  earth  upon  its  axis  with 
such  evenness  of  motion  that  we  experience  no  jar  or 
shock. 

Every  reader  has  had  similar  experiences  with  motions 
on  the  earth's  surface.  A  sleeping-car  passenger  awakes 


Rotation  of  the 
sphere. 


A  sleeping  car. 


The  Heavens  and  their  Apparent  Revolution.      43 

suddenly  in  the  middle  of  the  night,  and  concludes 
by  the  comparative  silence  and  the  absence  of  noticeable 
jarring  that  his  train  is  stopping  at  some  station.  Look- 
ing out  of  the  window  he  sees  a  freight  train  apparently 
slowly  backing  on  the  next  track.  The  truth  is  that  the 
freight  train  is  at  rest,  while  his  own  train  is  just  start- 
ing up. 

A  passenger  steamer  leaves  Chicago  at  night  ;  having  A  steamer, 
gotten  fairly  out  of  the  harbor,  it  turns  in  order  to  head 
in  a  certain  direction.  While  it  is  turning  the  lights  of 
the  city  and  the  stars  in  the  sky  appear  to  the  passen- 
gers to  be  revolving  in  the  opposite  direction  to  that  in 
which  they  themselves  are  turning. 

Conceive  the  axis  of  the  earth  to  be  prolonged  till   The  olgs 
it  strikes  the  celestial  sphere.    The  north  end  of  the  axis 
strikes  near  Polaris,  at  a  point  called  the  north  celestial 
pole.    The  south  end  strikes  at  the  opposite  point  of  the 
celestial   sphere,    called   the   south   celestial   pole.       A 
straight  line  joining  these  two  points  is  the  axis  of  the 
celestial  sphere,  about  which  it  appears  to  rotate.   If  there  / 
were  a  bright  star  at  each  pole,  and  we  could  see  both  of 
them  at  the  same  time,  we  should  have  little  difficulty  in 
getting  an  accurate  idea  of  just  how  the  heavens  rotate. 

A  line  drawn  from  the  eye  of  the  observer  parallel  to 
the  earth's  axis,  and  prolonged  to  the  celestial  sphere, 
would  strike  so  near  the  centers  of  the  stars,  which 
we  have  imagined  to  be  at  the  celestial  poles,  that  no  as- 
tronomer could  measure  the  deviation.  We  are  therefore 
entirely  justified  in  laying  down  the  following  principle 
to  guide  our  thinking  in  this  matter  of  the  apparent 
daily  rotation  of  the  star-sphere  : 

The  star-sphere  appears  to  turn  once  a  day  about  an 
axis  drawn  from  the  observer' s  eye  to  the  north  celestial 
which  is  in  the  vicinity  of  Polaris. 


44 


A  Study  of  the  Sky. 


Observations 
and  records. 


We  may  now  locate  the  north  celestial  pole  more  ac- 
The  north  pole,  curately  than  by  saying  that  it  is  in  the  vicinity  of 
Polaris.  The  star  which  is  situated  at  the  bend  of  the 
handle  of  the  Great  Dipper  is  called  Mizar.  Let  the 
eye  travel  slowly  from  Polaris  directly  toward  Mizar  ; 
when  it  has  gone  a  distance  equal  to  one  fourth  of  the 
distance  between  the  Pointers,  it  has  reached  the  north 
celestial  pole. 

But  the  explanation  which  has  just  been  given  does 
not  suffice  for  our  needs.  The  motion  of  rotation  can 
be  well  grasped  only  by  repeated  observations  of 
the  heavens.  Since  we  now  purpose  to  get  acquainted 
with  the  heavens,  gaining  knowledge  which  will  be  a 
source  of  delight  throughout  life,  we  must  not  only 
observe,  but  also  record  some  of  our  observations,  that 
they  may  be  the  better  fixed  in  mind.  A  common 
blank  book  will  answer  our  needs. 

A  picture  of  the  Great  Dipper  is  first  to  be  drawn. 
We  get  it  and  Polaris  well  in  mind  by  looking  at  them 
a  minute  or  two.  Polaris  is  considerably  brighter  than 
any  other  star  within  fifteen  degrees  of  it,  and  is  almost 
directly  north  of  us,  about  half  way  from  the  horizon  to 
the  zenith.  It  is  also  at  the  end  of  the  handle  of 
the  Little  Dipper,  which  is  shown  in  the  figure.  The 
distance  from  Polaris  to  the  furthest  corner  of  the  bowl 
of  the  Little  Dipper  is  nearly  twenty  degrees,  and 
the  curved  handle  is  about  twelve  degrees  in  length. 

We  first  locate  Polaris  on  a  page  of  the  blank  book, 
and  then^draw  a  faint  line  directly  down  from  it,  to  rep- 
resent a  vertical  line  ;  we  also  draw  a  horizontal  line 
similarly.  These  are  only  to  assist  in  getting  the  Dip- 
per correctly  located.  The  Pointers  are  next  drawn, 
care  being  taken  that  the  distance  from  Polaris  to 
the  nearest  Pointer  shall  be  five  times  the  distance 


The  first  draw- 
ing. 


Polaris  and  the 
Pointers. 


The  Heavens  and  their  Apparent  Revolution.      45 


between  the  Pointers.  Then  come  the  other  two  stars 
of  the  bowl  in  their  proper  relative  positions,  and  lastly 
the  handle.  After  this  the  Little  Dipper  may  be  drawn. 

The  picture  now  resembles  Fig.  n,  except  that  the 
vertical  and  horizontal  lines 
may  not  lie  in  the  same  posi- 
tions with  reference  to  the  stars 
as  in  the  diagram,  and  that 
the  dotted  lines  have  not  been 
drawn.  The  date  of  obser- 
vation and  the  time  (within 
five  minutes)  when  the  drawing 
was  finished  are  recorded.  If 
the  drawing  was  made  early  in 
the  evening,  another  similar 
one  should  be  made  just  before 
retiring  for  the  night.  A  com- 
parison of  the  two  will  show 
that  the  Dippers  have  shifted 
their  positions  with  reference 
to  the  vertical  and  horizontal 
lines.  After  watching  the  Dip- 
pers for  two  or  three  nights  the  answers  to  the  following 
queries  may  be  written  down  in  the  note-book  : 

Is  Polaris  as  bright  as  either  of  the  Pointers  ?    Is  any 
star  in  the  bowl  of  the  Little  Dipper  brighter  than  the  °-ueries- 
faintest  in  the  bowl  of  the  Great  Dipper  ?     How  many 
stars  can  be  seen  within  the  bowl  of  the  Great  Dipper  ? 
There  is  a  faint  star,    called  Alcor,  which   is  within  a 
degree   of   Mizar ;    what   is   its   color  ?      The   distance 
from  Alcor  to  Mizar  is  what  fraction  of  a  degree  ?  What 
is  the  color  of  each  of  the  Pointers  (white,  yellowish, 
reddish,  bluish)?     Is  the  Great  Dipper  higher  up  late  h> 
the  evening  than  early  ?    At  some  time  during  the  night 


FIG.  ii. — THE  Two  DIPPERS. 


46 


A  Study  of  the  Sky. 


How  the 
Dipper  moves. 


Motion  of 
other  stars. 


would  the  bowl  of  the  Great  Dipper  be  near  the  zenith  ? 
If  so,  would  the  handle  be  east  or  west  of  the  bowl 
at  that  time  ?  At  about  what  time  on  the  day  of  obser- 
vation was  the  bowl  underneath  Polaris  ?  Where  was  the 
bowl  of  the  Little  Dipper  with  reference  to  Polaris,  when 
the  large  bowl  was  underneath  ?  If  a  watch  were  held 
between  your  eye  and  Polaris  in  such  a  position  that  you 
looked  squarely  at  its  face,  would  the  extremity  of  the 
minute  hand  travel  around  the  face  in  the  same  direction 
in  which  the  Dippers  go  around  the  pole-star,  or  in  the 
opposite  direction  ?  Twelve  hours  after  the  time  of  your 
first  observation  where  would  the  Great  Dipper  be  with 
reference  to  Polaris  ?  Does  Mizar  keep  at  the  same  dis- 
tance from  Polaris  ?  Does  the  bowl  of  the  Great  Dipper 
ever  disappear  below  your  horizon  ?  Does  this  bowl 
move  downward,  when  at  the  left  of  the  pole-star  as  you 
face  it  ?  If  it  were  below  Polaris  would  it  appear  to  be 
moving  toward  your  right  as  you  face  it  ?  Is  there  any 
time  during  the  twenty-four  hours  which  are  consumed 
by  a  revolution  of  the  star-sphere  when  Alcor  appears 
to  be  exactly  in  line  between  Mizar  and  Polaris  ? 

Did  you  ever  see  the  moon  close  to  either  Dipper  ?  If 
you  turn  your  back  on  the  pole-star  and  face  southward 
will  a  star  off  in  the  south  appear  to  be  traveling  toward 
your  right  ?  If  you  face  westward  and  look  up  at  a  star 
near  the  zenith,  will  that  star  be  moving  westward  down 
the  vault  of  the  sky  ?  Will  its  distance  from  Polaris  ap- 
parently alter  as  the  hours  of  the  night  roll  on  ?  Will 
the  star  slide  straight  down  the  sky,  as  if  endeavoring  to 
reach  the  horizon  by  the  shortest  path,  or  will  it  veer  off 
toward  the  north  ?  A  star  has  just  risen  close  by 
the  east  point  of  the  horizon  ;  as  it  climbs  the  sky  will  it 
go  straight  toward  the  zenith,  or  will  it  veer  off  toward 
the  south  ?  Are  there  any  stars  except  Polaris  and  those 


The  Heavens  and  their  Apparent  Revolution.     47 

in  the  Dippers  which  never  disappear  below  your 
horizon  ? 

If  the  reader  is  not  sure  about  the  answer  to  any 
of  these  queries,  he  should  watch  the  heavens  until 
doubt  gives  way  to  certainty. 

The   expression    ' '  celestial  sphere, ' '   which  we  have 

,  r        1        1  ,      .      ,  .  The  definition 

used  so  freely,  has  a  technical  meaning  among  astrono-  of  the  celestial 
mers.  They  define  it  as  a  sphere  whose  radius  is  in- 
finite, so  that  the  remotest  stars  lie  far  within  it.  The 
apparent  position  of  any  object  on  this  sphere  is  the 
point  where  a  line  drawn  from  the  observer's  eye 
through  the  object,  and  extended  to  an  infinite  distance, 
pierces  the  sphere. 

Our  first  and  most  difficult  lesson  in  astronomy  is  at 
an  end. 


CHAPTER  III. 

THE    CONSTELLATIONS    IN    GENERAL. 

"  Look  how  the  floor  of  heaven 
Is  thick  inlaid  with  patines  of  bright  gold  ; 
There's  not  the  smallest  orb  which  thou  behold'st, 
But  in  his  motion  like  an  angel  sings  ; 
Still  quiring  to  the  young-eyed  cherubins." 

— Shakespeare. 

MEN  of  the  earliest  ages  were  quick  to  perceive  that 
there  were  certain  striking  groups  of  stars,  some  of 

The  menagerie,  which  rudely  resembled  men  and  animals.  To  these 
they  gave  names,  according  to  their  fancy.  Even  the 
most  savage  nations  have  not  failed  to  name  certain 
groups.  A  celestial  globe  of  the  present  day  is  covered 
with  a  veritable  menagerie  of  monsters,  the  names  of 
which  are  largely  taken  from  Greek  mythology.  We 
cannot  trace  the  origin  of  these  names  satisfactorily  ; 
some  of  them  occur  in  the  most  ancient  writings.  Many 
of  the  groupings  are  highly  artificial,  and  were  ap- 
parently devised  to  immortalize  the  heroes  and  heroines 
of  mythological  tales. 

Andromeda.  The  story  of  Andromeda  is  a  case  in  point.  She  was 

a  daughter  of  Cepheus,  a  king  of  the  Ethiopians.  Her 
mother,  Cassiopeia,  imprudently  boasted  that  the  beauty 
of  Andromeda  excelled  that  of  the  Nereids,  who  were 
lovely  divinities  inhabiting  the  depths  of  the  Mediter- 
ranean. Incensed  at  this,  the  Nereids  betook  them- 
selves to  Poseidon,  the  chief  divinity  of  that  sea,  and 
prevailed  upon  him  to  visit  Libya  by  an  inundation, 

48 


The  Constellations  in  General.  49 

and  further  to  send  a  sea-monster  to  ravage  the  unhappy 
land.  An  oracle  promised  deliverance  if  Andromeda 
were  given  up  to  the  rapacious  maw  of  the  leviathan. 
The  clamor  of  his  people  obliged  Cepheus  to  yield,  and 
Andromeda  was  chained  to  a  rock. 

It  so  happened  that  a  brave  youth,  Perseus  by  name, 
had  just  accomplished  the  daring  feat  of  slaying  Medusa, 
one  of  the  Gorgons.  Her  snaky  head,  which  turned 
the  beholder  to  stone,  was  borne  aloft  by  Perseus  in 
triumph.  From  her  blood  sprang  Pegasus,  the  winged 
horse.  As  Perseus  journeyed  homeward  through  the 
air,  with  his  horrid  trophy,  he  spied  Andromeda. 
Everybody  will  admit  that  the  only  proper  thing  for  this 
prehistoric  knight  to  do  was  to  kill  Cetus,  the  sea- 
monster,  break  the  chains  of  Andromeda,  and  marry 
her.  He  proved  equal  to  all  these  demands,  though 
her  color  did  not  match  his. 

Among  the  stars  we  now  find  Andromeda,  Cassiopeia, 
Cepheus,  Cetus,  Perseus  with  Medusa's  head  still  in  his 
hand,  and  Pegasus. 

The  Great  Dipper,  to  which  we  paid  so  much  atten- 

,       t  .  .     '  The  Great  Bear, 

tion  in  the  last  chapter,  is  a  portion  of  the  constellation 

of  the  Great  Bear.  One  of  the  Greek  legends  is  that 
Jupiter,  who  had  a  penchant  for  falling  in  love  with  fair 
women,  wooed  the  nymph  Callisto,  and  metamorphosed 
her  into  a  bear,  lest  Juno  should  enliven  his  domestic 
affairs  unduly.  But  Juno  was  not  deceived  by  this  ruse, 
and  persuaded  Diana  to  slay  the  bear.  Jupiter  then 
gave  Juno  a  standing  lesson  about  meddling  with  his 
royal  prerogatives  by  placing  Callisto  among  the  stars, 
under  the  name  of  Arctos,  the  Greek  word  for  bear. 

The  Iroquois  Indians,  when  America  was  discovered,    Thelro  uois 
are  said  to  have  called  this  star-group  Okouari,  which 
signifies  bear. 


A  Study  of  the  Sky. 


The  Chariot. 


The  ancient 
constellations. 


Christian 
heavens. 


Heraldic 
constellations. 


The  zodiac. 


The  Greeks  also  applied  the  designation  ' '  The 
Chariot ' '  to  the  Great  Dipper.  The  bowl  may  be  con- 
sidered as  the  body  of  the  chariot,  and  the  handle  as  the 
pole.  This  conceit  survives  in  England,  where  the 
appellation  ''King  Charles'  Wain"  is  used,  and  in 
France,  where  it  is  often  called  ' '  David' s  Chariot. ' ' 

Ptolemy,  who  did  so  much  in  systematizing  the 
astronomy  of  his  day,  has  transmitted  to  us  forty-eight 
constellations,  which  are  now  called  the  ' (  ancient  con- 
stellations, ' '  and  are  accepted  and  retained  largely  on 
account  of  their  historic  interest.  Their  names  are 
thoroughly  woven  into  astronomical  literature,  both 
popular  and  scientific. 

Some  attempts  have  been  made  to  dispossess  the 
ancient  heroes  of  their  happy  hunting  grounds.  Early 
in  the  eighth  century  the  Venerable  Bede  advocated  a 
plan  for  Christianizing  the  heavens.  Henceforth  the 
apostles  were  to  have  conspicuous  places  in  the  sky. 
Peter  was  to  take  the  place  of  the  Rarri;  as  was  fitting, 
and  the  other  disciples  were  to  be  distributed  around 
the  zodiac  after  him. 

In  the  seventeenth  century  Professor  Weigel,  of  the 
University  of  Jena,  proposed  that  a  series  of  heraldic 
constellations  be  formed,  the  zodiac  being  composed  of 
the  arms  of  the  twelve  foremost  families  in  Europe. 
But  this  attempt  to  displace  the  old  scheme,  as  well  as 
all  others,  failed. 

The  zodiac,  or  zone  of  animals,  is  a  belt  sixteen 
degrees  wide,  which  extends  around  the  sky  like  the 
stripe  on  a  croquet  ball.  From  antiquity  onward  much 
attention  has  been  paid  to  the  constellations  in  it. 
Imagine  that  a  line  from  the  center  of  the  sun  to  the 
earth's  center  is  prolonged  through  the  earth,  and 
extended  till  it  meets  the  celestial  sphere. 


The  Constellations  in  General.  51 

While  the  earth  travels  round  the  sun  in  its  annual 
journey,  the  extremity  of  this  line  traces  a  circle  on  the 
celestial  sphere.  The  name  of  the  circle  is  '  'the  ecliptic. ' '  The  ecliptic. 
To  an  eye  situated  at  the  sun's  center  the  earth  would 
appear  to  travel  around  the  ecliptic.  To  an  eye  placed 
at  the  earth's  center  the  sun  would  similarly  appear  to 
course  along  the  ecliptic,  taking  a  year  to  make  the 
complete  circuit,  passing  through  the  zodiacal  constel- 
lations in  succession.  The  ecliptic  lies  in  the  middle  of 
the  zodiac,  which  extends  eight  degrees  each  side  of  it. 
As  we  watch  the  sun,  moon,  and  planets,  they  always 
appear  to  lie  in  the  zodiac. 

The  ancients  gave  to  certain  small  and  conspicuous 
groups  special  names,  such  as  the  Pleiades  and  the  Hy-   Othernames- 
ades.      Individual  stars  of  pronounced  brightness  were 
also  named.     We  glance  for  a  moment  at  some  interest- 
ing facts  concerning  the  Pleiades. 

The  Pleiades  were  often  used  in  connection  with 
the  calendar  by  ancient  peoples,  and  are  still  employed 
thus  by  some  savage  tribes.  This  group  of  stars  is  situ- 
ated near  the  ecliptic.  The  sun,  therefore,  in  his  annual 
journey,  gets  so  near  them  at  one  time  of  the  year  that 
they  cannot  be  seen  for  several  days.  Six  months  after 
this  time,  when  the  sun  has  gone  half  way  round 
the  heavens,  it  is  opposite  the  Pleiades,  so  that  they  rise 
when  it  sets,  and  vice  versa.  From  Hesiod  we  learn 
that  the  Greeks  in  his  day  accounted  the  winter  season 
as  commencing  when  the  Pleiades  were  seen  low  down 
in  the  east  soon  after  sunset,  and  the  summer  season 
when  they  set  soon  after  the  sun. 

The  Society  Islanders  are  said  to  have  divided  the  The  Society 
year  into  two  parts,   according  to  the  position  of  the  Islanders- 
Pleiades.       That   half  of   the  year   during  which  they 
could   be   seen   early   in  the  evening  was  called    "the 


A  Study  of  the  Sky. 


The  Druids. 


The  Peruvians. 


Australian 
savages. 


Pleiades  above. ' '  The  other  half  was  ' '  the  Pleiades 
below. ' ' 

The  rising  of  the  Pleiades  at  sunset  occurs  about  No- 
vember i.  On  that  night  was  one  of  the  most  note- 
worthy festivals  of  the  Druids,  in  which  they  celebrated 
the  destruction  and  rejuvenation  of  the  world.  The 
sacred  fire,  which  had  burned  continuously  in  the  temple 
during  the  past  year,  was  extinguished,  and  then  the 
spirits  of  those  who  had  died  during  the  year  embarked 
in  ghostly  array  in  the  boats  which  were  to  take  them  to 
the  seat  of  judgment,  where  the  god  of  the  dead  appor- 
tioned to  each  his  lot.  In  the  church  calendar  of  to-day 
November  i  is  known  as  All  Saints'  Day.  The  preced- 
ing evening  is  Hallowe'en.  The  following  day  is  All 
Souls'  Day,  and  is  celebrated  in  the  Roman  Catholic 
Church  by  supplications  for  the  souls  of  the  pious  dead. 

A  festival  commemorative  of  the  dead  is  held  at  this 
time  of  year  in  many  parts  of  the  world.  The  Peruvi- 
ans visit  the  tombs  of  their  relatives,  to  bring  food 
and  drink  for  the  departed,  and  to  lament  with  plaintive 
songs  and  weeping.  In  India  the  month  of  November 
is  called  the  month  of  the  Pleiades,  and  a  Hindu  festival 
of  the  dead  is  celebrated  about  the  middle  of  the  month. 
The  Persians  once  named  the  month  after  the  angel 
of  death. 

Australian  savages  are  said  still  to  hold  a  ' '  corro- 
boree  "  at  this  season,  in  honor  of  the  Pleiades,  which, 
say  they,  "  are  very  good  to  the  black  fellows."  These 
occasions  are  also  festivals  of  the  dead  ;  the  savages 
paint  white  stripes  upon  their  bodies  in  such  fashion  that 
they  appear  like  skeletons,  as  they  execute  weird  noc- 
turnal dances  about  their  fires. 

From  Prescott's  "  History  of  the  Conquest  of  Mex- 
ico" we  learn  that  the  Mexicans  celebrated  a  great 


The  Constellations  in  General.  53 

cycle  of  fifty-two  years,  the  celebration  occurring  on 
a  November  night.  There  was  a  tradition  that  the  The  Mexicans, 
world  was  once  destroyed  at  this  time.  When  the 
shades  of  evening  fell,  and  the  Pleiades  rose,  the  cere- 
monies began.  As  this  group  of  stars  approached  the 
zenith  a  human  sacrifice  was  offered,  to  avert  a  repeti- 
tion of  the  dreadful  calamity.  When  once  the  Pleiades 
had  passed  the  highest  point  of  their  course,  and  were 
seen  to  be  descending  in  the  west,  the  gloom  and 
dismay  of  the  people  gave  place  to  rejoicing. 

The  names  now  used  for  most  of  the  stars  of  the  first 
magnitude  come  from  Greek  or  Latin  sources,  and 

Proper  names 

are  significant.  Thus  Arcturus  comes  from  the  Greek,  of  stars, 
and  means  "  the  bear-driver."  Antares,  the  red  star  in 
the  heart  of  the  Scorpion,  shows  by  its  name  that  it 
is  the  rival  of  Ares  (the  Greek  name  for  Mars,  the  ruddy 
planet).  The  word  Sirius  is  probably  derived  from  the 
Greek  eetpios,  and  therefore  signifies  ' '  the  scorching 
one."  Quite  a  number  of  names  were  given  by  the 
Arabians.  Aldebaran  signifies  ' '  the  follower  "  ;  it  is 
supposed  to  have  received  this  designation  because  it 
rises  shortly  after  the  Pleiades.  Altair,  ' '  the  flying 
eagle,"  is  the  brightest  star  in  the  constellation  of 
Aquila,  the  Eagle.  Betelgeuse  is  a  modification  of  the 
Arabic  Ibt-al-jauza,  which  means  ' '  the  giant' s  shoul- 
der" ;  the  star  is  located  in  the  shoulder  of  Orion,  the 
mighty  hunter. 

Stars  which  had  no  proper  names  were,  up  to  the  be- 
ginning of  the  seventeenth  century,  usually  designated 
by  referring  to  their  positions  in  the  constellations. 
Thus  we  read  of  the  star  in  the  right  knee  of  Bootes,  or 
in  the  club  of  Hercules.  This  inadequate  plan  is 
happily  no  longer  in  vogue. 

In  1603  Bayer  published  a  star  atlas  in  which  he  made 


54 


A  Study  of  the  Sky. 


The  modern 
system  of 
naming. 


Flamsteed's 
numbers. 


Catalogues. 


use  of  the  letters  of  the  Greek  and  Roman  alphabets. 
According  to  this  system  the  brightest  star  in  the 
constellation  Lyra  is  called  Alpha  Lyrae.*  The  next 
star  in  that  constellation,  in  point  of  brightness,  is  Beta 
Lyrae.  When  the  letters  of  the  Greek  alphabet  have 
been  exhausted,  and  there  remain  stars  yet  unlettered, 
the  Roman  alphabet  is  taken  up. 

If  all  the  letters  of  the  Roman  alphabet  have  been 
used  and  there  yet  remain  naked-eye  stars  which  are 
unnamed,  numbers  assigned  by  the  astronomer  Flam- 
steed  are  employed.  At  present  every  star  visible  to  the 
unassisted  eye  can  be  referred  to  by  letter  or  number. 
The  system  of  numbers  is  entirely  independent  of  the 
letters,  every  star  in  a  given  constellation  having  a  num- 
ber, even  though  it  may  have  been  previously  called  by 
a  letter.  The  numbers  were  not  given  in  order  of 
brightness.  When  the  daily  revolution  of  the  stars 
brought  the  constellation  Taurus  to  the  meridian  of 
Greenwich,  the  first  naked-eye  star  which  crossed  the 
meridian  was  called  by  Flamsteed  i  Tauri ;  the  next  star 
was  2  Tauri,  etc. 

The  hundreds  of  thousands  of  faint  stars  whose  posi- 
tions have  been  determined  by  modern  astronomers 
receive  their  names  from  their  current  numbers  in  star 
catalogues.  For  instance  the  1 634th  star  in  Lalande's 
catalogue  is  known  as  Lalande  1634.  The  stars  in  all 
modern  catalogues  are  arranged  in  the  order  in  which 
they  cross  the  meridian  of  any  place,  without  reference 
to  the  constellations  within  whose  boundaries  they  lie. 

What  does  a  modern  catalogue  tell  about  each  star 
which  it  contains  ?  This  question  cannot  well  be 
answered  until  we  learn  the  meanings  of  two  simple  ex- 


*  Lyra  is  the  genitive  case,  or,  as  we  would  say  in  English,  the  possessive 
case  of  the  Latin  word  lyra. 


The   Constellations  in   General,  55 

pressions,  "right  ascension"  and  "declination."  These 
terms  are  analogous  to  those  used  in  geography  in 
locating  places  on  the  earth.  As  there  is  a  terrestrial 
equator,  so  there  is  a  celestial  equator,  as  heretofore 
explained.  As  the  latitude  of  a  city  is  its  distance, 
expressed  in  degrees,  from  the  terrestrial  equator,  so  the 
declination  of  a  star  is  its  distance  from  the  celestial 
equator.  There  is  a  prime  meridian  on  the  earth,  e.  g. , 
the  meridian  of  Greenwich,  from  which  longitude  is 
reckoned  eastward  or  westward  ;  there  is  also  a  certain 
celestial  meridian  which  passes  through  the  celestial 
poles,  and  cuts  the  celestial  equator  at  a  particular  point 
called  the  "  vernal  equinox,"  the  location  of  which  we 
shall  explain  more  particularly  hereafter.  As  the  city  of 
Denver  has  a  longitude  of  seven  hours,  so  some  star  has 
a  right  ascension  of  seven  hours.  While  longitude  on 
the  earth  is  reckoned  either  eastward  or  westward  from 
the  principal  meridian,  the  right  ascension  of  a  star  is 
reckoned  eastward  only. 

In  a  star  catalogue  we  expect  to  find  three  things 
stated  about  each  star,  its  right  ascension,  its  declina- 
tion, and  its  brightness.  An  explanation  of  the  method 
of  estimating  brightness  will  be  given  in  the  next  chapter. 

The  letters  of  the  Greek  alphabet  are  given  below,  for 
the  benefit  of  those  who  may  not  know  them.     They  will  The  Greek 
slip  easily  into  the  memory,  in  the  process  of  learning  the 
constellations  which  are  given  in  the  next  three  chapters. 


0. 

Alpha. 

£ 

Iota  (io'ta). 

P 

Rho. 

0 

Beta  (ba'ta). 

k 

Kappa. 

ff 

Sigma. 

r 

Gamma. 

X 

Lambda. 

T 

Tau  (tou). 

8 

Delta. 

!* 

Mu  (mu). 

O 

Upsilon'. 

e 

Epsilon7. 

V 

Nu  (nu). 

¥ 

Phi  (phe). 

f 

•a 

Zeta  (za'ta). 

£ 

Xi  (kse). 

7, 

Chi  (ke). 

If 

Eta  (a'ta). 

0 

Omicron/. 

$ 

Psi  (pse). 

0 

Theta  (tha'ta). 

7T 

Pi  (pe). 

CO 

Ome^ga. 

CHAPTER    IV. 

THE    CONSTELLATIONS    FOR   JANUARY    AND    FEBRUARY. 

"  Ye  quenchless  stars  !  so  eloquently  bright, 
Untroubled  sentries  of  the  shadowy  night, 
While  half  the  world  is  lapp'd  in  downy  dreams, 
And  round  the  lattice  creep  your  midnight  beams, 
How  sweet  to  gaze  upon  your  placid  eyes, 
In  lambent  beauty  looking  from  the  skies  !  " 

—  Montgomery. 


A  review.  WE  are  now  ready  to  confront  the  sky  for  the  purpose 

of  getting  a  hailing  acquaintance  with  the  most  interest- 
ing of  the  star-groups.  For  we  have  already  learned 
something  of  their  origin,  of  the  methods  of  naming  the 
stars  in  each  constellation,  and  the  way  of  locating  them 
by  right  ascension  and  declination.  We  have  also  ob- 
tained ideas  concerning  the  apparent  daily  motion  of  the 
star-sphere,  and  can  therefore  .foresee,  to  a  certain  ex- 
tent, the  effect  of  this  motion  on  the  position  of  a  con- 
stellation during  the  successive  hours  of  the  night. 

Every  reader  will  not  find  time  to  learn  all  the  constel- 

lations described   in  this   and   the   next  two  chapters. 

Three  constei-    ^ut  eveiT  one  should  form  the  acquaintance  of  at  least 

lationsamonth.   three  constellations  a  month.     Therefore  the  three  most 

conspicuous  constellations  of  those  given  for  each  month 

are  named  in  black  letter.     One  may  read  the  remainder 

of  the  book  before  the  constellation  work  is  finished. 

The  work  is  so  arranged  that  it  may  be  done,  a  little  at 

a  time,  during  the  first  six  months  of  the  year.      During 

the  vacation  months  of  summer  the  pleasant  evenings 

56 


The  Constellations  for  January  and  February.      57 

will  tempt  the  observer  to  review  those  constellations 
which  are  then  visible,  and  thus  to  fasten  them  in  the 
memory. 

Only  those  stars  which  form  the  characteristic  con-   „ 

J  The  character- 

figuration  of  each  constellation  are  given  in  the  illustra-  '^  configura- 
tion of  it.  Many  other  adjoining  stars,  which  are 
generally  fainter,  are  within  the  arbitrary  boundaries  of 
the  constellation,  as  laid  down  on  standard  maps  of  the 
heavens.  To  these  extra  stars  we  pay  no  attention  ;  an 
attempt  to  learn  them  would  be  a  waste  of  energy,  as 
not  even  professional  astronomers  are  familiar  with  them. 
It  is  not  advisable  to  learn  the  Greek  letter  for  every 
star.  If  any  particular  star  interests  the  reader 
especially,  it  is  well  to  remember  its  name.  For 
example,  Epsilon  Lyrse  is  a  famous  quadruple  star, 
which  consists  of  two  adjoining  pairs  of  revolving  suns, 
and  is  used  as  a  test  of  acuteness  of  vision.  It  is  best  to 
learn  the  names  of  those  bright  stars  which,  like  Sirius, 
Arcturus,  and  Vega,  are  among  the  most  splendid 
objects  in  the  sky.  Such  names  are  printed  in  the 
diagrams. 

The  faintest  star  which  can  be  seen  by  an  average  eye 
is  said  to  be  of  the  sixth  magnitude.  A  star  which  is  \ stellar 
two  and  one  half  times  as  bright  as  this,  and  can  be 
seen  easily,  is  of  the  fifth  magnitude.  A  fourth  magni- 
tude star  is  two  and  one  half  times  as  bright  as  one  of 
the  fifth.  Thus  the  scale  of  magnitudes  is  ascended  till 
we  reach  the  first  magnitude.  Fewer  than  twenty  of 
the  fixed  stars  are  bright  enough  to  be  rated  as  of  the 
first  magnitude,  and  some  of  them  are  much  brighter 
than  others.  A  standard  first  magnitude  star  is  one 
hundred  times  as  bright  as  one  of  the  sixth  magnitude. 
The  magnitudes  of  the  stars  are  indicated  by  the  symbols 
given  on  the  next  page  : 


A  Study  of  the  Sky. 


Estimation  of 
distance. 


Hints. 


Observation 
exercises. 


First  magnitude,         • 
Second  magnitude,  -•- 
Third  magnitude,      ^f 
Fourth  magnitude,   -^- 
Fifth  magnitude,         • 

Two  stars  which  appear  in  a  diagram  of  the  same 
magnitude  may  seem  to  the  observer  quite  different. 
Both  stars,  for  instance,  may  be  given  of  the  third  mag- 
nitude, though  one  is  only  a  little  fainter  than  magnitude 
three  and  one  half,  while  the  other  is  nearly  as  bright  as 
magnitude  two  and  one  half.  For  small  distances  the 
observer  may  use  as  a  measuring  rod  the  distance  be- 
tween the  Pointers,  which  is  close  to  5°.  For  longer 
distances  it  will  be  convenient  to  remember  that  the 
distance  from  the  extremity  of  the  handle  of  the  Great 
Dipper  to  the  Pointer  at  the  top  of  the  Dipper  bowl 
is  26°. 

In  learning  a  constellation  one  should  first  familiarize 
himself  with  the  illustration  given  in  the  book,  studying 
it  till  he  can  make  a  rude  sketch,  showing  the  relative 
positions  of  the  stars.  Having  this  mental  picture,  he 
can  face  the  sky  with  a  good  degree  of  assurance,  and  will 
generally  have  little  difficulty  in  picking  out  the  stars 
desired.  The  constellations  will  not  usually  appear  the 
same  side  up  as  in  the  book.  But  if  the  observer 
imagines  a  line  drawn  on  the  sky  from  the  north  pole, 
or  practically  from  Polaris,  directly  toward  the  desired 
constellation  and  through  its  center,  this  line  will  run 
from  the  center  of  the  upper  edge  of  the  diagram  to  the 
center  of  the  lower  edge. 

After  the  description  of  each  constellation  are  given  a 
few  queries,  the  answers  to  which  may  be  written  in  the 
observer's  note-book.  If  two  or  more  persons  observe 


The  Constellations  for  January  and  February .       59 

together,  the  work  will  prove  quite  fascinating.      But  in 
answering  the  queries  one  should  never  allow  his  judg-   independence, 
ment  to  be  swayed  by  that  of  a  companion.     The  eyes 
of  one  person  are  not  like  those  of  another,  and  each 
should  put  down  what  his  own  eyes  reveal. 

Ursa  Major. 

The  Great  Dipper,  with  which  we  have  already  be- 
come familiar,  is  a  portion  of  Ursa  Major,  the  Great  Bear. 


Y* 


^ 


^  . 


FIG.  12. — URSA  MAJOR. 

About  9  p.  m.  during  any  evening  in  January  this 
constellation  is  found  at  the  right  of  Polaris.  The  Bear 
appears  at  that  time  to  be  balancing  himself  upon  the 
tip  of  his  tail.  The  star  o  (Fig.  12)  marks  the  tip  of  the 
creature's  nose.  The  animal  is  short  one  fore  leg,  but 
map-makers  are  accustomed  to  supply  the  missing  mem- 
ber, despite  the  absence  of  available  stars.  Each  of  the 
three  existing  feet  is  marked  by  a  couple  of  stars  ;  the 


6o 


A  Study  of  the  Sky. 


The  Bear's  tail. 


The  Dipper. 


Mizar. 


components  of  each  pair  are  less  than  two  degrees  apart. 
£  and  fc  mark  the  front  foot  ;  A  and  /JL  mark  the  forward 
hind  foot.  The  remaining  hind  foot  is  located  by  v  and 
£ .  These  three  pairs  of  stars  lie  almost  in  a  line,  the 
central  pair  being  about  twenty  degrees  from  each  of 
the  others. 

The  handle  of  the  Dipper  is  the  tail  of  the  Bear,  and 
is  of  appropriate  length  'for  a  cow.  This  anomaly,  we 
are  told  by  an  old  writer,  is  due  to  the  fact  that  Jupiter 
lifted  the  bear  by  its  tail,  when  he  raised  it  to  the  sky. 

The  stars  in  the  Dipper  have  received  proper  names, 
which  are  sometimes  used  even  by  astronomers,  who, 
except  in  the  case  of  the  stars  of  the  first  magnitude, 
usually  prefer  the  Greek  letter  nomenclature.  «  Ursse 
Majoris  is  Dubhe  ;  ft  is  Merak  ;  Y  is  Phecda  ;  d  is  Me- 
grez  ;  e  is  Alioth  ;  C  is  Mizar ;  -Q  is  Benetnasch  or  Alkaid. 

Mizar  is  one  of  the  finest  of  double  stars,  as  seen  with 
a  small  telescope,  and  was  the  first  of  such  objects 
which  the  telescope  revealed  ;  it  was  discovered  in  1650, 
soon  after  the  invention  of  that  instrument.  These  two 
magnificent  suns,  one  of  the  second,  the  other  of  the 
fourth  magnitude,  are  slowly  revolving  about  their  com- 
mon center  of  gravity.  The  time  of  a  complete  revolu- 
tion is  roughly  estimated  at  20,000  years.  In  1889 
Prof.  E.  C.  Pickering*  discovered  by  means  of  observa- 
tions with  the  spectroscope  that  the  brighter  of  the  two 
components  of  Mizar  is  itself  a  double.  The  two  stars 
composing  it  are  thought  to  make  one  revolution  about 
one  another  in  one  hundred  and  four  days,  the  diameter 
of  their  orbit  being  about  140  million  miles.  The  mass 
of  the  system  is  forty  times  that  of  the  sun.  Near 
Mizar  is  the  faint  star  Alcor,  which  the  average  eye 
should  see  without  difficulty. 

*  Director  of  the  Harvard  College  Observatory. 


The  Constellations  for  January  and  February .       61 

According  to  mythology,  Ursa  Major  is  the  nymph 
Callisto,  who  was  so  pleasing  in  Jupiter's  eyes  that  Juno  Mythology. 
became  jealous.  One  version  of  the  legend  is  that 
Jupiter  changed  Callisto  to  a  bear,  to  avoid  Juno's 
jealousy  ;  another  version  is  that  Juno  took  revenge 
upon  her  rival  by  changing  her  into  a  bear.  Being  un- 
willing to  lose  his  favorite  in  this  way,  Jupiter  trans- 
ported her  to  the  stars. 

What  is  the  magnitude  of  Alcor,  and  its  distance  Queries 
(fraction  of  a  degree)  from  Mizar  ?  Which  is  the 
brightest  star  in  the  Dipper  ?  How  many  stars  are  vis- 
ible within  the  bowl  of  the  Dipper  ?  Twelve  hours  after 
the  time  of  sketching  the  constellation,  what  is  its 
position  ? 

Ursa  Minor. 

At  7  p.  m. ,  on  any  evening  early  in  January,  the 
Little  Bear  is  suspended  by  his  tail,  the  end  of  which  is 
fastened  at  Polaris  (Fig.  13).  It  has  been  suggested 
that  the  inordinate  length  of  his  tail  is  an  illustration  of 
the  Darwinian  law  of  adap- 
tation to  environment,  the  Q-j 
tail  having  been  stretched 
in  the  process  of  swinging  ~W"" 
the  Bear  around  once  in  ^ 
every  twenty-four  hours, 
for  hundreds  of  years.  &  "*  X>X  ^  ^ 

This  star-group  is  com-  £f  ™  ; 

monly  called  the  Little 
Dipper ;  the  handle  of  the 
utensil  is  a  neat  curve  con- 

.    .         .  .  FIG.  13. — URSA  MINOR. 

taming  four  stars,  including 

the  one  by  which  it  is  joined  to  the  bowl.     The  two   The  Little 
brightest  stars  in  the  bowl  are  called  the  ' '  Guardians  of  Dlpper> 
the  Pole. ' '     The  constellation  guided  the  Phenicians  in 


62 


A  Study  of  the  Sky. 


Polaris. 


The  north 
celestial  pole. 


A  double  star. 


Description. 


their  voyages  on  the  Mediterranean,  just  as  the  pole-star 
now  affords  to  a  seaman  a  method  of  checking  the  in- 
dications of  his  compass,  should  he  fear  that  it  is  awry. 
Polaris  is  one  of  the  nearest  of  our  neighbors  among 
the  fixed  stars.  Yet  a  railway  train,  speeding  continu- 
ously at  the  rate  of  sixty  miles  an  hour,  would  require 
600  millions  of  years  to  reach  it.  So  enormous  a 
distance  is  very  difficult  to  measure,  and  is  subject 
to  considerable  uncertainty  arising  from  the  unavoidable 
errors  inherent  in  even  the  most  careful  measurements 
of  experienced  astronomers. 

(The  north  pole  of  the  heavens  lies  on  a  line  from  Po- 
laris to  Mizar,  being  a  little  more  than  a  degree  from  the 
former.  Polaris  has  not  always  been  the  pole-star. 
Because  of  the  attractions  of  the  sun  and  moon  upon  the 
equatorial  protuberance  of  the  earth,  the  direction  in 
which  the  axis  of  the  earth  points  is  continually  chang- 
ing. The  result  is  that  the  north  celestial  pole  moves 
in  a  circle  on  the  surface  of  the  sphere.  One  revolution 
is  made  in  25,800  years.  The  circle  passes  near  Vega, 
in  the  constellation  of  the  Lyre,  its  center  appearing  to 
lie  about  half  way  from  Polaris  to  Vega,  not  quite  on 
a  line  joining  them.  Twelve  thousand  years  hence  Vega 
will  be  the  pole-star,  unless  some  unforeseen  catas- 
trophe gives  an  unexpected  shift  to  the  earth's  axis. 

Polaris  is  a  double  star,  having  a  companion  of  mag- 
nitude 9.5,  which  can  be  detected  with  a  telescope 
of  two  or  three  inches'  aperture.  By  the  "aperture"  of 
a  telescope  is  meant  the  diameter  of  the  object-glass, 
which  is  the  lens  at  the  large  end  of  the  telescope. 
Cassiopeia. 

The  pole-star  is  midway  between  the  Great  Dipper 
and  a  striking  group  of  five  stars,  three  of  which  are  of 
the  second  magnitude,  the  other  two  being  of  the  third. 


The  Constellations  for  Jamiary  and  February.       63 

The  group  resembles  a  dilapidated  W,  and  consists  of  ^dilapidated 
the  stars  /?,   «,  -f,  <*,  £,  shown  in  Fig.    14.      By  adding  K 
the  figure  is  brought  to  a  rude  likeness  to  a  broken- 
backed  chair,    f  and  K  forming  the  seat  of  the  chair, 
while  d  and  e  outline  its  back. 

Cassiopeia  is  often  called   "The  Lady  in  the  Chair," 
and  one    is    thus 
led    to   suppose 
that  she  is  seated 

/      N 

in  the  chair.    But  *\^  f* 

the    map-makers  \  -~€h^ 

have    ordered  Tf  \ 

otherwise,  and 

the     queen    dis- 

dains    to    sit    on 

anything     more  FIG.  ^.-CASSIOPEIA. 

substantial  than  the   ether.      /3,   a,  p,   and  fc   form   her 

body;  d  lies  in  her  knee,  and  i  marks  her  foot.     Her  ^J^f/ty in 

hands  are  upraised,  as  if  in  prayer  to  the  gods  to  spare 

her  beautiful  daughter  Andromeda,  the  story  of  whose 

danger  and  rescue  has  already  been  told. 

Less  than  two  degrees  from  fc,  on  the  opposite  Tycho.sstar 
side  of  it  from  ^,  appeared  in  November,  1572,  a 
new  star,  which  was  bright  enough  to  be  seen  in  full 
sunshine.  Tycho  perceived  it  while  out  for  an  evening 
stroll,  and  thenceforth  observed  its  changes  assiduously. 
In  December  its  fires  paled  perceptibly,  and  after  a 
lapse  of  sixteen  months  it  became  invisible  to  the  naked 
eye.  When  it  first  appeared  it  inspired  great  terror 
among  the  ignorant,  and  was  thought  to  presage  the 
end  of  the  world. 

An  opera-glass  reveals  many  beautiful  regions  in  Cas- 
siopeia, where  the  stars  besprinkle  the  sky  like  diamond  c 
dust.     A  line  drawn  from  K,  to  /?,  and  prolonged  half  as 


64 


A  Study  of  the  Sky. 


Double  star. 


Queries. 


Description. 


far  again,  terminates  at  a  cluster  of  small  stars  discov- 
ered by  Caroline  Herschel,  the  sister  and  assistant  of  Sir 
William  Herschel.  A  degree  from  3  another  fine  field 
of  stars  is  located.  Any  one  who  has  a  small  telescope 
may  spend  considerable  time  pleasurably,  exploring  the 
Milky  Way  in  and  adjacent  to  Cassiopeia. 

Between  a  and  f  lies  >?,  a  star  of  the  fourth  magni- 
tude, which  is  comparatively  near  us,  its  light  taking 
not  much  over  twenty  years  to  come  to  us.  It  has  a 
colored  companion  too  close  to  it  to  be  detected  without 
a  telescope.  The  hue  vies  with  that  of  the  chameleon, 
having  been  called  by  various  astronomers  green, 
purple,  blue,  red,  and  lilac.  Such  a  diversity  is  best  ex- 
plained by  changes  in  the  star  itself,  though  such 
changes  seem  improbable. 

Is  ri  in  a  direct  line  between  a  and  y  ?  How  many 
stars  are  at  the  end  of  a  line  drawn  from  ft  through 
the  middle  point  between  a  and  >y,  and  prolonged  nearly 
an  equal  distance  ?  li  ft  is  now  at  the  left  of  the  pole, 
and  as  high  above  the  horizon  as  Polaris,  will  it  be  lower 
two  hours  hence,  or  higher  ? 

Pegasus. 

Pegasus,  the  winged  horse,  is  a  very  large  constella- 
tion, the  conspicuous  portion  of  which  is  a  large  square, 
whose  sides  average  15°  in  length  (Fig.  15).  Three  of 
the  four  stars  in  the  square  are  of  the  second  magnitude. 
One  corner  of  the  square  lies  at  the  extremity  of  a  line 
drawn  from  Polaris  to  ft  Cassiopeise,  and  prolonged  an 
equal  distance  beyond  ft.  The  star  at  this  corner  is 
common  to  the  two  figures  of  Pegasus  and  Andromeda, 
and  is  universally  called  a  Andromedse.  The  same  line 
prolonged  14°  further  meets  y,  which  is  at  another 
corner  of  the  square.  The  square  lies  west  of  the  zenith, 
about  half  way  down  to  the  horizon,  at  7  p.  m.  in  the 


The  Constellations  for  January  and  Febniary.       65 

middle  of  January,  its  uppermost  side  being  the  one  just 
described.  The  square  is  the  body  of  the  horse,  which  The  square, 
has  no  hind  quarters.  At  the  opposite  corner  of  the 
square  from  «  Andromedae  lies  a  Pegasi.  A  line  from 
the  first  of  these  stars  to  the  second,  prolonged  an  equal 
distance,  passes  ^9 

through  C  in  the 
neck,  and  termi- 
nates at  0,  which 
is  at  the   top  of       / 
the  head,     e  is  in      / 
the   nose.     The    ^~ 
two    fore  legs  *\ 

start    at    /?,    and  NVC 

are   marked   by  X  Jf 

dotted  lines    in  N*v_-'' 

the  diagram. 

A  line  from  0  FlG-  IS.-PEGASUS. 

to  e,  prolonged  a  little  more  than  half  its  length,  reaches 
a  globular  cluster,  which  can  be  seen  with  a  good  opera-  A  star  cluster- 
glass,  and  is  one  of  the  finest  condensed  clusters  in  the 
sky.  Star  crowds  upon  star,  and  the  center  of  the  clus- 
ter is  a  blaze  of  glory,  which  seems  to  defy  separation 
into  individual  stars.  We  have  here  a  system  of 
thousands  of  suns,  each  of  which  undoubtedly  moves 
under  the  attraction  of  all  the  others.  The  cluster  is  at 
least  one  hundred  millions  of  millions  of  miles  away. 

When  Perseus  had  killed  the  Gorgon  Medusa,  Pega- 
sus, the  winged  horse,  sprung  from  her  blood.  Rising 
to  the  abodes  of  the  immortals  he  became  Jupiter's 
charger  for  a  time.  When  Bellerophon  wished  to  slay 
the  Chimsera,  it  was  necessary  for  him  to  bestride  Pega- 
sus. Minerva  gave  him  a  golden  bridle,  with  which  he 
caught  the  horse  as  he  was  drinking  at  the  well  Pirene. 


66  A  Study  of  the  Sky. 

The  Chimsera  vanquished,  Bellerophon  attempted  to  as- 
cend to  heaven  on  the  back  of  his  winged  steed.  But 
Jupiter  sent  a  gad-fly,  which  stung  the  animal  and 
caused  him  to  throw  his  rider.  Pegasus  then  flew  on  to 
the  stars. 

How  many  stars  can  you  count  on  a  moonless  night, 
within  the  boundaries  of  the  square  ?  Is  *  double  to  the 
naked  eye  ?  Does  the  square  set  at  the  west  point  of 
the  horizon,  or  north  of  that  point?  Which  is  the 
shortest  side  of  the  square  ? 

Aquarius. 

Aquarius  is  low  in  the  west  in  January,  in  the  evening, 
and  should  be  looked  for  as  soon  as  the  sky  has  become 
fairly  dark.*  A  line  from  /5  Pegasi  to  C  Pegasi,  when 

'•£**       ^ 

,-''  XNX 

f *•        v 


FIG.  16.— AQUARIUS. 

prolonged  two  thirds  of  its  length,  reaches  an  equilateral 
triangle,  composed  of  three  stars  of  the  third,  fourth,, 
and  fifth  magnitudes  respectively,  in  the  center  of  which 
lies  a  third  magnitude  star.  The  sides  of  the  triangle  are 
3°  long;  the  four  stars  resemble  a  Y  (Fig.  16).  This  is 

*  Should  the  reader  fail  4o  get  hold  of  this  constellation  because  it  is  low  in 
the  west,  further  study  of  it  may  be  postponed  until  early  summer,  when  it  is 
seen  in  the  east,  late  in  the  evening. 


The  Constellations  for  January  and  February .       67 

the  water- jar  of  Aquarius ;  from  it  flows  a  stream,  which 

winds  its  way  southward  and  eastward  into  the  mouth  of 

the  Southern  Fish,  where  lies  the  first  magnitude  star 

Fomalhaut  (Fo-ma-lo).    The  stars  w,  17,  p,  and  C  form  the 

V  or  water-jar.     The  stream  flowing  down  to  Fomalhaut   Fomalhaut. 

follows  the  dotted  line  in  the  diagram  through  </>,  4',  etc. 

The  line  is  marked  by  several  groups  of  faint  stars,  near 

v';,  «,  etc.     /5  Pegasi  lies  nearly  midway  between  Polaris 

and    Fomalhaut.     At   the  right   of   the  Y   lies  a  rude 

short-handled  dipper,  which  the  observer  will  fail  to  find 

unless  he  looks  very  early  in  the  evening,  and  as  near 

the  first  of  the  month  as  practicable.      Most  of  the  stars 

which  stand  guard  between  the  dipper  and  the  stream, 

that  the  fish  be  not  defrauded  of  the  water,  belong  to 

the  constellation.     Lines   joining  the   brighter  ones  of 

them  form   a   configuration    not   unlike  the   outline   of 

South   America  ;    c2  is   at   Cape    Horn,    the    continent 

touching  the  stream  at  this  point.     C  in  the  center  of  the 

Y  lies  close  to  the  celestial  equator,  and  therefore  sets 

very  near  the  west  point  of  the  horizon. 

There  is  a  remarkable  nebula  situated  i°  from  v 
toward  e,  which,  in  a  large  telescope,  exhibits  a  resem-  nSuia." 1 
blance  to  the  planet  Saturn.  It  appears  to  be  a  world 
or  system  of  worlds  in  formation.  Should  it,  in  the  ages 
to  come,  become  a  gigantic  Saturn-like  form,  having  a 
central  globe,  surrounded  by  a  thin  flat  ring  composed 
of  a  myriad  of  smaller  worlds,  how  magnificent  and  awe- 
inspiring  a  spectacle  ! 

Aquarius  is  thought  by  some  to  represent  the  youth  Mythology 
Ganymede,  the  most  beautiful  of  mortals,  whom  Jupiter 
snatched  to  Mount  Olympus  to  be  his  cup-bearer. 
With  a  fine  appreciation  of  the  distress  of  the  bereaved 
parents  he  endeavored  to  assuage  their  grief  by  a 
present  of  a  team  of  fine  horses  ! 


Queries. 


Description. 


68 


A  Study  of  the  Sky. 


How  many  faint  stars  can  be  seen  close  to  0  ?  Are 
there  five  groups  of  faint  stars  (from  two  to  four  stars  in 
a  group)  lying  in  the  stream,  between  <p  and  Fomalhaut? 
When  the  water-jar  is  nearly  setting  in  the  west,  what 
two  stars  in  it  lie  most  nearly  in  a  horizontal  line  ? 
Pisces. 

Like  Aquarius,  this  constellation  is  largely  composed 
of  faint  stars,  the  brightest  one  being  of  only  the  third 
magnitude.  But  the  group  lies  in  a  dull  region  of  the 


•  * 

>. 


*'"*' 


* 


•• 


FIG.  17.— PISCES. 


sky,  so  that  the  ribbon  joining  the  two  fishes  can  be 
readily  traced  (Fig.  17).  The  southernmost  fish  is  com- 
The  circlet.  posed  of  a  circlet  of  seven  stars,  5°  or  6°  in  diameter. 
Three  of  these  stars,  f,  i,  and  A,  are  of  the  fourth  mag- 
nitude; the  distance  from  £  to  A  is  4°.  f  is  6°  from  each 
of  the  other  stars.  The  center  of  the  circlet  lies  12° 
south  of  the  southern  side  of  the  square  of  Pegasus  ;  e  is 
equidistant  from  a  Pegasi  and  f  Pegasi.  From  t  in  the 
circlet  a  row  of  stars  runs  eastward  to  a  a  distance  of 


The  Constellations  for  January  and  February.      69 

35°,  and  is  a  portion  of  the  ribbon  joining  the  two  fish. 
a.  is  called  El  Rischa,  the  Knot,  and  lies  10°  west  of  the 
western  side  of  a  well-marked,  five-sided  polygon,  the 
average  length  of  one  side  of  which  is  5°.  The  polygon, 
as  we  shall  learn  hereafter,  is  the  head  of  Cetus,  the  sea- 
monster.  At  the  Knot  the  ribbon  turns  at  a  sharp 
angle,  and  runs  northwesterly  a  distance  of  30°,  ter- 
minating in  a  coarse  group  of  faint  stars,  which  may  be 
found  by  prolonging  a  line  from  ft  Pegasi  to  «  Androm- 
edae  eastward  15°,  a  little  more  than  its  own  length. 

The  vernal  equinox,  which  is  the  point  in  the  sky  at  The  vernai 
which  the  sun's  center  appears  to  lie,   when  it  crosses  ec*umox- 
the  celestial  equator  in  March,  and  ushers  in  the  spring, 
lies  in  a  barren  spot  of  sky  just  east  of  the  circlet  of  stars 
forming  one  fish.     A  line  from  Y  to  ^>  extended  as  far 
again,  ends  at  the  equinox. 

FEBRUARY     CONSTELLATIONS. 
Andromeda. 

This  constellation  is  found  early  in  the  evening  in  the  D  \  \\  n 
northwest,  a  has  already  been  mentioned  as  one  corner 
of  the  square  of  Pegasus  ;  it  is  located  by  drawing  a  line 
from  Polaris  to  ft  Cassiopeia^,  and  prolonging  it  an  equal 
distance.  A  line  from  Polaris  to  the  middle  point  be- 
tween e  Cassiopeiae  and  t  of  the  same  constellation,  pro- 
longed an  equal  distance,  ends  at  Y  (Fig.  18).  The 
bright  stars  ft  and  <5  lie  nearly  in  line  between  a  and  Y  >* 
these  four  form  one  side  of  the  maiden's  form,  a  being 
in  the  head  and  Y  m  one  foot,  ft  is  in  her  waist  and  3 
at  one  shoulder.  Her  outstretched  arms  run  from  n  to 
A,  and  from  d  to  y. 

A  line  from  ft  across  her  waist  to  /*,  when  prolonged   The  great 
an  equal  distance,  ends  at   the  great  nebula,  which  is  nebula- 
plain  to  the  naked  eye.     Here  is  a  storehouse  of  un- 


A  Study  of  the  Sky. 


A  double  star. 


Queries. 


Description. 


created  worlds,  which  is  vast  beyond  all  human  compre- 
hension. The  entire  solar  system,  if  flung  into  this 
mighty  abyss  of  chaotic  matter,  would  be  as  a  few 

grains  of  sand  in  a 
wagon-load. 

Y  is  a  fine  double 
star,  as  seen  with  a 
small  telescope,  the 
components  being 
of  widely  different 
hues,  the  smaller 
one  being  of  the 
fifth  magnitude  ;  a 
large  telescope  splits 
the  small  star  in 
two,  showing  that 
it  is  composed  of 
two  revolving  suns. 
The  mythological 


a 


FIG.  18.— ANDROMEDA. 


story  of  Andromeda  has  been  told  at  length  already, 
and  is  therefore  omitted  here. 

What  is  the  color  of  ?  ?  Which  is  the  brighter,  /3  or  f  ? 
Is  the  great  nebula  round  or  oval  to  the  naked  eye  ? 

Aries. 

Aries  lies  in  the  northwest  early  in  the  evening  in 
February.  A  line  from  Polaris  to  Y  Andromedae,  when 
prolonged  nearly  20°,  terminates  at  «,  the  brightest  star 
in  the  small  triangle  composed  of  «,  /?,  and  Y  (Fig.  19). 
The  distance  from  a  to  Y  is  only  5°.  The  entire  triangle 
is  located  in  the  head  of  the  Ram.  East  of  this  triangle, 
between  it  and  the  Pleiades,  are  scattered  a  number 
of  faint  stars,  which  are  sprinkled  quite  at  random  over 
the  Ram's  body. 


The  Constellations  for  January  and  February  .       71 

According  to  Grecian  mythology  a  ram  with  a  golden   Mythoiogy. 

fleece,    the    gift    of    Mercury, 
\\  flew  with   two  children,   Helle 

x    N  and  Phrixus,  over  a  sea.     Helle 

\    X  was  s°  unfortunate  as  to  drop 

off    into   the   sea,     which   was 


accordingly  named  the  Helles- 
x     }          pont  (the  sea  of  Helle).     The 
famous   Argonautic  expedition 
was   for   the   recovery   of    the 

FIG.  19.— ARIES. 

Cetus. 

Cetus  should  be  studied  early  in  February,  and  as 
soon  as  it  is  dark,  for  the  constellation  is  then  in  the 
southwest,  and  sets  early.  The  monster  resembles  a 
walrus  ;  his  head 

alone  is  above  the     i--^--. 

^ 
celestial  equator.     • 

The    body    of  ^~--y-'y 
the   leviathan    is  ^ 

marked  by  a  kite-  *>5** 

shaped    figure 

formed  of  the  \  ^ 

stars  /?,   i?,   0,    Z,  cT""        ">r 

and  T  (Fig.  20).  \ 

P  lies  on  a  line  &" \ 

from      Polaris  */  "' •*= 

'jV1 

through    C    An- 
dromeda (which  FIG*  20-CETUS- 

is  in  one  of  the  lady's  arms),  and  is  nearly  45°  beyond  Description. 
the  latter.     The  kite  is  20°  long  from  P  to  C.     The  tip 
of  the  tail  of  Cetus  lies  at  «,  11°  northwest  of  p.     The 
position  of  the  pentagon  forming  the  head  (a,  y,  etc.)  is 
shown  in  the  diagram,  C  being  equi-distant  from  p  and  f, 


A  Study  of  the  Sky. 


Mira. 


Mythology. 


Queries. 


Description. 


Pleiades  and 
Hyades. 


but  not  directly  in  line  with  them.  u  marks  the  ex- 
tremity of  a  flipper.  A  line  from  a  to  p,  when  extended 
10°  further  westward,  nearly  strikes  «  Piscium. 

A  little  more  than  half  way  from  C  to  y  lies  n.  This 
star  has  received  the  proper  name  Mira,  the  Wonderful, 
because  of  the  remarkable  changes  of  its  brightness.  It 
is  visible  to  the  naked  eye  only  three  months  in  a  year  ; 
on  one  occasion  in  the  eighteenth  century  it  became 
as  bright  as  a  first  magnitude  star,  r  is  one  of  the  most 
rapidly  moving  stars  known.  It  is  traveling  across  the 
kite  toward  ??,  which  it  will  reach  in  19,000  years,  if  it 
keeps  on  at  a  uniform  rate. 

Cetus  is  the  sea-monster,  frequently  called  ' '  the 
Whale,"  that  was  to  devour  Andromeda,  by  order  of 
Neptune.  But  Perseus  intercepted  and  killed  him. 

Which  is  the  brighter,  a  or  /?  ?     Does  the  naked  eye 
show  that   o   consists   of   more   than   one   star?      Less 
than  half  a  degree  from  C  lies  a  star  of  the  fifth  mag- 
nitude ;  does  it  lie  within  the  kite  ? 
Taurus. 

Taurus,  the  Bull,  is  noteworthy  because  it  contains 
the  Pleiades,  the  Hyades,  and  the  first  magnitude  star 
Aldebaran.  It  resembles  Pegasus,  in  that  only  its  head 
and  fore  shoulders  have  reached  the  sky.  Nevertheless 
it  makes  a  brave  show  of  charging  at  Orion,  the  mighty 
hunter,  of  whom  we  have  still  to  learn. 

The  Pleiades  are  readily  recognized.  They  are  25° 
east  of  a  Arietis.  Ten  degrees  east  of  the  Pleiades,  and 
less  than  that  distance  south  is  a  V-shaped  figure, 
which  constitutes  the  face  of  the  Bull,  and  contains 
Aldebaran.  The  horns  are  between  15°  and  20°  long, 
their  tips  being  /?  and  C  (Fig.  21).  The  V-shaped 
group  is  called  the  Hyades.  Both  the  Pleiades  and  the 
Hyades  should  be  examined  with  an  opera-glass,  as 


The  Constellations  for  January  and  February .      73 

they  contain   many  stars,  which   are  thus  brought  out 

well.     Six  of  the  Pleiades  should  reveal  themselves  to 

the  unaided  eye.     On   a  good  night,  when  the  moon 

is  below  the  horizon,   a  dozen  stars   may  be  seen  by 

an  acute  eye.     Alcyone,   the  brightest  of  the  Pleiades,    Alcyone. 

was  once  surmised  to  be  the  center  of  the  universe,  but 

the  theory  had  no  sufficient  foundation  and  was   soon 

abandoned.      Photography   has    shown   that   shreds   of 


V 

A 

?-4~V 

*        "I  v. 


FIG.  21. — TAURUS. 

nebulosity  cling  to  many  of  the  Pleiades,  as  if  they  were 
the  remnants  of  an  original  nebula  from  which  the 
cluster  has  been  evolved. 

In  the  eye  of  the  Bull  glows  a,  which  is  usually  called  Aidebaran. 
by  its  Arabic  name  Aidebaran.     Its  distance  from  us, 
according  to  some  of  the  latest  measures,  is  about  100 
millions  of  millions  of  miles. 

Taurus,  in  common  with  the  majority  of  the  constella- 

.  »  , 

tions  of  the  zodiac,  is  one  of  the  ancient  Egyptian  star- 


74  A  Study  of  the  Sky. 

groups,  and  was  associated  with  the  bull  Apis.  The 
Greeks  described  it  as  a  mild  and  milk-white  bull,  into 
which  Jupiter  changed  himself  when  he  wished  to  seek 
the  favor  of  beautiful  Europa.  The  Pleiades  were  seven 
in  number,  being  the  daughters  of  Atlas,  and  sisters 
of  the  Hyades  ;  one  fell  in  love  with  a  mortal,  and 
hid  herself  from  shame.  When  Atlas  had  joined  the 
other  Titans  in  an  attack  upon  Jupiter,  and  had  been 
conquered,  he  was  condemned  to  uphold  the  sky.  His 
sad  fate  led  the  Pleiades  to  make  way  with  themselves. 
Both  Atlas  and  Pleione,  the  father  and  mother,  were 
placed  in  the  sky  in  the  same  group  with  their  devoted 
children. 

What  is  the  color  of  Aldebaran  ?  What  star  in 
the  V  is  double  to  the  naked  eye  ?  Is  any  one  of  the 
Pleiades  double,  as  seen  with  an  opera-glass  ? 

Orion. 

One  who  can  look  upon  this  magnificent  constellation 
without  a  thrill  of  delight  has  no  eye  for  the  beauties  of 
the  heavens.  At  8  p.  m.  in  the  middle  of  February  it  is 
on  the  meridian  in  the  south,  half  way  from  the  horizon 
to  the  zenith.  It  resembles  the  figure  of  the  mighty 
hunter,  who  stands  facing  us  (Fig.  22);  with  his  right 
hand  he  brandishes  a  club,  with  which  he  is  about  to 
Description.  smite  charging  Taurus  full  in  the  face.  The  top  of  the 
club  is  marked  by  two  stars  of  the  fifth  magnitude,  2^° 
apart,  which  point  nearly  at  C  Tauri,  which  is  5°  west  of 
them,  at  the  top  of  one  of  the  Bull's  horns.  The  belt  of 
the  giant  is  marked  by  the  three  second  magnitude  stars 
d,  e,  and  C.  The  length  of  the  belt,  which  is  often  called 
the  Ell  and  Yard,  is  3°  ;  it  points  westward  toward  the 
Pleiades,  and  eastward  toward  Sirius,  the  brightest  of 
the  fixed  stars.  On  either  side  of  the  belt,  at  distances 
of  about  10°,  lie  Betelgeuse  in  the  right  shoulder, 


The  Constellations  for  January  and  February.       75 

and  Rigel  in  the  left  foot.     These  are  respectively  a  and 

p.     In  the  left  shoulder  is  y,  also  called  Bellatrix,  and  in 

the  right  knee  is  fc.     The  head  is  marked  by  a  small 

isosceles  right  tri-       ^  9 

angle.      Over   the         /     / 

left  arm  is  thrown        /    / 

the  skin  of  a  lion.      •  / 

From  the  belt  dan-  •  •  ^  The  sword. 

gles    a     sword,     \\ 

which   consists    of       \\ 

the   third    magni-         •  -^  ^ 

tude  star «,  and  two  \      ^''     \ 

faint  stars  immedi-  " 


ately  above  it  ;    a  --, 

good   eye  sees  in  *  , 

the    sword    four  \  • 

faint  stars,  in  a  \         fj 

row.    The  first  star 

above  t  is  0,  which 

is  involved  in  the  ,'v  \ 

i      <9<-         \ 

great   nebulaof  /    ~&6 

Orion.       It  has  a 

hazy    appearance  ^ 

to  the  naked  eye. 

_,1  ,          .     .  FIG.  22.— ORION. 

The   celestial 

equator  passes  nearly  through  d,  the  uppermost  star  in 
the  belt. 

Betelgeuse  and  Rigel  must  be  bodies  of  amazing  mag-  Betelgeuse 
nitude,  for  they  are  so  far  away  that  astronomers  have  and  Ri^el- 
not  been   able   to   measure   their  distances  ;    yet   they 
are  among  the  brightest   of   the   stars.     It   is   safe   to 
say  that  their  distances  exceed  200  million  million  miles. 

The  great  nebula,  which   is  situated   in   the   sword,    The    eat 
is  the  most  marvelous  object  of  its  kind  in  the  entire  nebuia- 


76 


A  Study  of  the  Sky. 


Mythology. 


Queries. 


Description. 


sky.  Even  an  opera-glass  reveals  a  little  of  the  central 
portion  of  it ;  in  a  large  telescope  its  magnificence 
baffles  description.  In  viewing  it  with  a  large  telescope 
it  is  well  to  point  the  telescope  just  west  of  the  nebula, 
and  allow  it  to  drift  through  the  field  of  view.  0,  which 
is  involved  in  the  nebula,  is  a  sextuple  star  ;  the  four 
brightest  stars  in  it  have  received  the  name  of  the 
Trapezium. 

The  Milky  Way  runs  hard  by  Orion,  and  has  appar- 
ently besprinkled  it  with  a  shower  of  starry  spray.  The 
entire  constellation,  seen  through  an  opera-glass,  is  well 
spangled  with  faint  stars. 

Orion  was  a  handsome  giant  and  great  hunter ; 
he  led  an  unhappy  life,  on  account  of  his  beauty  and 
accomplishments.  He  lost  his  eyesight  in  consequence 
of  his  first  love  affair  ;  after  he  recovered  it  by  looking 
full  at  the  rising  sun,  Aurora,  the  goddess  of  the  dawn, 
fell  in  love  with  him  and  carried  him  off.  According  to 
another  account  no  less  a  personage  than  Diana,  whose 
heart  was  supposed  to  be  Cupid  proof,  became  en- 
amored of  him.  Her  indignant  brother  Apollo  took 
occasion  one  fine  day  to  tease  her  about  her  skill  in 
archery,  and  asserted  that  she  could  not  hit  a  certain 
shining  mark,  which  bobbed  on  a  distant  wave.  She 
hit  it,  and  lo  !  it  was  Orion's  head. 

What  is  the  color  of  Betelgeuse  ?  What  is  the  color 
of  Rigel  ?  Does  the  middle  star  in  the  belt  lie  above  or 
below  a  line  connecting  the  other  two  ?  Are  there  two 
stars,  or  three,  in  a  line  a  degree  south  of  the  belt,  and 
parallel  to  it,  the  line  being  as  long  as  the  belt  ? 

Auriga. 

A  little  less  than  half  way  from  Bellatrix  (j  Orionis) 
to  Polaris  is  Capella,  a  first  magnitude  star,  which  is  the 


angle  of  fourth  magnitude       ;  A  A 


The  Constellations  for  January  and  February  .       77 

leading  luminary  of  Auriga.  It  is  at  one  corner  of  an  ir- 
regular five-sided  figure,  the  other  corners  being  at  /3,  /? 
Tauri,  0,  and  £  (Fig.  23).  The  distance  from  Capella 
to  /5  Tauri  is  20°.  The  remainder  of  the  constellation 
consists  chiefly  of  inconspicuous  stars,  lying  on  the 
north  and  east  sides  of  the  five-sided  polygon.  Auriga 
signifies  "the  charioteer."  A  line  from  6  to  /5,  pro- 
longed  northward  an  equal  distance,  meets  the  fourth 
magnitude  star  d,  which  is  ^ 

in  the  man'  s  head.  His 
feet  are  at  «  and  ft  Tauri. 
Near  Capella  is  a  little  tri- 

* 

stars  ;  two  sides  of  it  are      i  v\ 

3°  long,  and  the  third  side   y  #  * 

only    i°.      One   vertex   of       N  * 

the  triangle  is  in  a  line  from          \  \ 

Capella  to  £.     The  triangle  \ 

represents  a  kid,  which  the  \  v 

charioteer    carries    in    his  \  „' 

arms.  ^  " 

Capella  is  comparatively 
near  us.     According  to  the  FlG"  ^--AURIGA. 

measures  of  one  of  the  highest  authorities*  its  distance    . 

Capella. 
is   170  millions   of   millions   of   miles.     Light   occupies 

twenty-nine  years  in  traversing  this  abyss.  Were  it  as 
close  as  our  sun,  it  would  be  sixty  times  as  bright  as 
he  is. 

About  half  way  from  6  to  P  Tauri  lies  a  fine  compact  A 
cluster  of  small  stars,  which  may  be  picked  up  with  an 
opera-glass,  in  which  it  looks  like  a  star  enveloped  in  a 
cloud  mantle. 

Near  ft   Tauri,    on   a   line    between   it   and   /?   there 

*  Dr.  W.  L.  Elkin,  of  Yale  College. 


A  Study  of  the  Sky. 


appeared  in  December,  1891,  a  new  star.  Professional 
Nova  Aurigse.  astronomers,  who  usually  have  their  eyes  glued  to  the 
eyepieces  of  their  telescopes,  when  observing,  failed  to 
see  it.  It  was  discovered  late  in  January,  1892,  by 
Dr.  T.  D.  Anderson,  a  Scotch  amateur.  Its  image 
was  afterward  found  on  photographic  plates  taken  in 
December  at  the  Harvard  College  Observatory.  At  the 
end  of  April  it  could  scarcely  be  seen  with  the  Lick 
36-inch  glass.  But  in  the  following  August  it  was 
bright  enough  for  a  three-inch  telescope,  and  had  ap- 
parently turned  into  a  nebula.  A  fuller  history  of  the 
wonderful  object  and  the  theories  of  astronomers  about 
it  will  be  given  later. 

Mythology.  The  mythological  history  of  this  constellation  is  very 

obscure.  Perhaps  the  charioteer  may  be  best  regarded 
as  Phaeton,  the  ambitious  youth  who  requested  his 
father  Helios  (the  sun)  to  let  him  drive  his  chariot 
across  the  sky  for  one  day.  The  horses  ran  away  and 
came  so  near  the  earth  that  it  was  nearly  set  on  fire.  A 
thunderbolt  from  Jupiter,  who  occasionally  did  a  sensible 
thing,  ended  the  young  man's  career. 

Queries.  What  is  the  color  of  Capella?     Is  Capella  brighter 

than  Betelgeuse  ? 


CHAPTER  V. 

THE    CONSTELLATIONS    FOR    MARCH    AND    APRIL. 

' '  Starry  crowns  of  heaven, 
Set  in  azure  night ! 
Linger  yet  a  little 
Ere  you  hide  your  light." 

—Procter. 

Gemini. 

A  LINE  from  Mizar  (C  Ursae  Majoris)  carried  down 
the  handle  of  the  Dipper  and  diagonally  across  the  bowl 
to  the  two  stars  which  lie  in  the  front  foot  of  the  Bear, 
when  prolonged  25°,  ends  near  Castor  and  Pollux. 
They  are  the  brightest  stars  in  Gemini,  and  are  respect- 
ively designated  by  the  letters  «  and  p  (Fig:  24).  Half 
way  between  Castor  and  the  head  of  Orion  is  /-*.  Some- 
what more  than  half  way  from  Pollux  to  Betelgeuse  is  y. 
a,  fi,  Y,  and  ft  are  the  four  corners  of  a  box-like  figure 
resembling  an  end  view  of  an  upright  piano.  The  key- 
board projects  from  C  to  A,  and  the  pedals  lie  between  y 
and  £.  17,  which  is  2*4°  west  of  //.,  is  a  variable,  rang- 
ing from  the  third  to  the  fourth  magnitude.  It  is  on  a 
line  from  p.  to  C  Tauri,  at  the  top  of  one  horn  of  the 
Bull.  The  heads  of  the  twins  contain  Castor  and  Pollux 
respectively.  Y  and  /*  mark  their  feet. 

The  summer  solstice,   which  is  the  point  where  the 

,  ,  .      .       .       ,  r  The  summer 

sun   appears   to   be,    when    it   is  farthest  north  of  the  solstice, 
equator  on  June  21,  is  2°  west  and  a  little  north  of  fjy 
close  by  a  star  of  the  fifth  magnitude. 

Castor  is  one  of  the  finest  double  stars  in  the  heavens ; 

79 


8o 


A  Study  of  the  Sky. 


Castor  and 
Pollux. 


so  bright  are  its  two  components  that  both  can  be 
readily  seen  in  daytime  with  a  ten-inch  telescope. 
Nearly  one  thousand  years  are  consumed  by  one  revo- 
lution of  this  majestic  pair.  Castor  is  approaching  us  at 
the  rate  of  eighteen  miles  a  second,  while  Pollux  keeps 
almost  at  the  same  distance  from  us. 

A  little  over  one  fourth  of  the  way  from  /j.  to  /5  Tauri 


Mythology. 


FIG.  24.— GEMINI.        '     „ 

is  a  splendid  cluster,  just  visible  to  the  naked  eye.  It  is 
composed  of  hundreds  of  faint  stars,  and  is  roughly 
circular  in  form.  The  apparent  diameter  of  the  circle  is 
two  thirds  that  of  the  full  moon. 

The  brothers  Castor  and  Pollux  were  two  mythologi- 
cal knights,  whose  chief  deeds  were  the  redressing  of 
various  wrongs.  They  were  thought  to  be  mighty 
helpers  of  men,  and  divine  honors  were  paid  to  them 
both  in  Sparta  and  at  Rome.  The  Romans  believed  that 
they  received  assistance  from  them,  while  fighting  the 


The  Constellations  for  March  and  April.         8 1 

Latins  at  Lake  Regillus.  In  Macaulay's  "Lays  of 
Ancient  Rx)me"  is  the  following  reference  to  their 
appearance  ; 

"  So  like  were  they,  no  mortal 

Might  one  from  other  know  ; 

White  as  snow  their  armor  was  ; 

Their  steeds  were  white  as  snow." 

According  to  one  version  of  the  story  Castor  was 
mortal,  while  Pollux  was  immortal.  When  Castor  was 
dying  Pollux  prayed  to  be  permitted  to  die  with  him. 
Jupiter  did  not  wish  to  grant  this  request,  but  rewarded 
their  attachment  by  allowing  them  both  to  spend 
alternate  days  on  Mount  Olympus  and  in  Pluto's  realm. 

Which  is  the  brighter,   Castor  or  Pollux?     What  is  Queries 
the  color  of  Castor?     Is  Capella  whiter  than  Castor? 
Perseus. 

This  constellation  should  be  hunted  up  early  in  the 
month,  as  soon  as  it  is  dark  ;  at  that  time  it  is  low  in 
the  northwest. 

A  little  more  than  half  way  from  Capella  to  ?  Androm -*" 
edse,  3°  north  of  the  line  joining  them,  lies  «,  which  is 
at  one  corner  of  a  small  quadrilateral,  the  cither  stars  of 
which  are  7%  c,  and  r.  A  line  from  Polaris  through  the 
center  of  this  quadrilateral,  when  prolonged  1 1  °  further, 
meets  /?,  which  is-  commonly  called  Algol,  the  Demon  The  Demon 
Star.  Its  magnitude  varies  from  the  second  to  the  fourth 
in  less  than  three  days.  The  rest  of  the  constellation 
is  best  learned  by  a  study  of  Fig.  25.  The  entire 
length  of  the  figure  from.  y\  to  C  is  27°.  The  head  of 
Medusa,  which  Perseus  carries  in  his  hand,  is  formed  of 
Algol  and  the  stars  near  it.  The  constellation  bears  no 
special  resemblance  to  a  man,  much  less  to  a  bear. 
It  might  be  a  fair  model  for  a  baboon. 

Near  the  middle  point  of  a  line  from  Y  to  d  Cassiopeiae 


82 


A  Study  of  the  Sky. 


A  cluster. 


Mythology. 


Queries. 


is  a  fine  double  cluster,  distinctly  visible  to  the  naked 
eye,  as  a  bright  spot  in  the  Milky  Way.  It  is  pretty  in 
an  opera-glass  and  fine  in  a  small  telescope.  Here 
hundreds  of  suns  are  bunched  together.  This  cluster  is, 
for  small  telescopes,  the  finest  visible  in  the  United 
States. 

Perseus    belonged   to   Jupiter's    numerous   family   of 

demigods.   Polydectes, 
*,  9      king  of  a  little  island, 
fell  in   love  with  Per- 
seus's    mother.       The 
young    man    opposed 
*0    the    king's    wishes  in 
this   matter,    and   was 
therefore  sent  to  fetch 
the  snaky  head  of  the 

x  i  monster  Medusa,  who, 

Tt  p^f  "&/      with  her  sister  Gor- 

/  -Ai  \          gons,   was  equipped 

_^>.  P         **&   with   tusk-like  teeth, 

j    **  brazen  claws,    and 

golden   wings.      So 
frightful  was  the  aspect 
of  a  Gorgon  that  any 
FIG.  25.-PERSEUS.  one  who  ^oked  on  her 

was  turned  to  stone.  Equipped  with  winged  sandals,  a 
magic  wallet,  a  helmet  which  made  him  invisible, 
a  sickle,  and  a  mirror  in  which  he  viewed  the  image  of 
the  monster,  he  accomplished  his  task.  In  his  home- 
ward voyage  through  the  air  he  rescued  Andromeda, 
the  Ethiopian  maiden,  and  married  her. 

Is  Algol  as  bright  as  ?  ?  Is  Algol  as  bright  as  «  ?  To 
what  star  in  Perseus  does  a  line  joining  the  centers  of 
the  two  clusters  mentioned  above  point  ? 


The  Constellations  for  March  and  April.         83 

Cancer. 

The  principal  stars  of  Cancer  form  an  inverted  Y  (Fig.    Degcr.  tion 
26),  which  is  on  the  meridian  at  9  p.  m.,  in  the  middle 
of  the  month.     The  total  length  i 

of  the  \  is  20°,  and  all  the  stars  9   t 

in  it  are  of  the  fourth  magni-  \ 

tude.  A  line  from  Polaris  to  « 
Ursae  Majoris,  when  prolonged  I 

40°  further,  ends  near  the  cen-  \ 

ter  of  the  A-     Near  the  middle  V 

point  of  a  line  joining  d  and  Y  9    ' 

lies  the  cluster  of  Praesepe,  the  / 

Bee-hive,  which  falls  an  easy 
prey  to  an  opera-glass.  To 
the  naked  eye  it  is  a  hazy  spot.  *  \ 

Two  degrees  west  of  «  is  an-  /  \ 

other  cluster  almost  visible  to  /  \ 

/  v 


the  naked  eye  ;  a  good  opera-         , 

glass  brings  it  out.  ~W^~  ' 

When  Hercules  was  having      '  Q 
a    desperate    battle    with    the 
nine-headed  Lernean  hydra,  a 
gigantic    crab    came     to     the  FlG>  26-~CANCER- 

assistance  of  the  hydra,  and  succeeded  in  wounding  the 
hero. 

Canis  Major. 

The  chief  jewel  of  this  group  is  Sirius,  brightest  of  the  Description, 
fixed  stars,  which  is  readily  found  by  prolonging  the 
belt  of  Orion  20°  eastward.  The  Dog  sits  upright, 
facing  his  master  Orion  (Fig.  28).  Sirius  burns  in  his 
head.  The  triangle  formed  by  <?,  e,  and  f]  is  in  his 
haunches.  /?  is  at  the  extremity  of  his  uplifted  fore  paw. 
He  is  evidently  in  the  attitude  of  begging  for  a  bite  of 


84 


A  Study  of  the  Sky. 


Sirius. 


Discovery  of  a 
companion. 


the  hare  under  Orion's  feet.  His  hind  legs  stretch  for- 
ward to  C  and  A.  A  fair  cluster,  barely  visible  to  the 
naked  eye,  is  situated  near  a  point  one  third  of  the  way 
from  Sirius  to  s.  A  small  telescope  reveals  a  red  star  in 
the  center,  which  is  brighter  than  its  companions.  3 
and  C  appear  double  in  an  opera-glass. 

Sirius  is  interesting  not  only  from  its  brightness,  which 
is  seven  times  as  great  as  that  of  Capella,  but  also  from 
the  fact  that  it  is  a  remarkable  double.  A  faint  com- 

panion,  fairly 
within  the  blaze 
of  glory  which 
surrounds  the 
telescopic  image 
of  the  bright  star, 
is  swung  around 
once  in  fifty-three 
years.  The  dis- 
tance of  Sirius 
from  us  is  fifty 
million  million 
miles;  light 
comes  from  it  to 
us  in  eight  years. 
The  companion 
was  discovered  by  Alvan  G.  Clark,  the  optician.* 
When  using  Sirius  to  test  the  1 8^ -inch  glass  now  at 
Dearborn  Observatory,  Evanston,  111.,  he  suddenly 
exclaimed,  "  Why,  father,  the  star  has  a  companion  !  " 
The  real  size  of  this  splendid  orb  may  be  inferred  from 
the  fact  that  it  radiates  forty  times  as  much  light  as  the 
sun.  A  more  complete  history  of  it  will  be  given  here- 
after, i 


4 


FIG.  27.— CANIS  MAJOR. 


*OfCambridgeport,  Mass. 


The  Constellations  for  March  and  April.         85 

Cants  Minor. 

There  are  but  two  bright  stars  in  this  asterism,  a  and  Description. 
/3  (Fig.  29).     «  is  commonly  called  Procyon.     Procyon 
is  27°  east  of  Betelgeuse  («  Orionis).     These  two  stars 
and  Sirius  form  an  equilateral 
triangle.    /?  is  4°  northwest  of 
Procyon.  x 

Procyon   is   interesting  for  x 

several  reasons  ;  it  is  one  of          ^x 
the    nearer   stars,  being   but    9  ^^tye/? 
seventy  million  million  miles  W. 

away.    It  is  moving  quite  rap-        FlG-  28.— CANIS  MINOR. 
idly,   for   a   fixed   star,    along  the  face  of  the  sky,   re-   proc  on 
quiring  only  i ,  500  years  to  traverse  a  distance  equal  to 
the  apparent  diameter  of  the  moon.     This  journey  is  not 
performed  in  a  straight,  but  in  a  wavy  line  ;  hence  it  is 
supposed  to  be  swung  from  side  to  side  by  the  attraction 
of  one  or  more  companions,  not  yet  discovered. 

Lepus. 
Lepus,  the  Hare,  lies  beneath   the   feet  of  Orion,  a 

*±  a  martyr  to  his  proclivities  Description. 

for  hunting.      With    a 

fj  i  good   opera-glass    one 

T^-^jF  may  see  f  double  (Fig. 

27).    The  most  remark- 
a       ^-  -~^-        able  object  in  the  con- 
stellation is  the  crimson 
*  star   R,    which   can   be 

^-  #  seen  with  an  opera -glass. 

x,     A     1i'n^     frr^m     a    thrOUgh 
o 


- 
'  "y~  ^>  when  prolonged  3 

FIG.  29.-LEPus.  strikes   it.      Like   most 

red  stars  it  is  variable,  ranging  in  magnitude  from  6.5 
to  8.5  in  a  period  of  14^  months. 


86 


A  Study  of  the  Sky. 


Description. 


Leo. 

This  is  a  striking  constellation,  composed  of  a  sickle 
and  a  large  right-angled  triangle  (Fig.  30).  It  is  just 
east  of  Cancer.  A  line  drawn  from  Polaris  to  n  Ursae 
Majoris,  which  lies  in  the  forward  hind  foot  of  the  Bear, 
prolonged  22°,  meets  f,  the  brightest  star  in  the  blade 
of  the  sickle.  A  line  from  Polaris  through  the  center  of 
the  bowl  of  the  Great  Dipper,  when  extended,  passes 
through  the  large  right  triangle,  which  is  east  of  the 
sickle.  ft,  at  one  vertex  of  the  triangle,  is  often  called 
Denebola  ;  a,  at  the  end  of  the  handle  of  the  sickle, 


+ 


FIG.  30.— LEO. 


Regulus. 


Double  stars. 


is  Regulus.  The  distance  from  Regulus  to  Denebola  is 
25°.  The  lion  is  crouching  ;  the  handle  of  the  sickle  is 
in  his  breast,  and  the  blade  in  his  head.  The  triangle  is 
in  his  haunches  ;  his  tail  and  hind  legs  are  represented 
by  a  few  scattered  stars  south  of  the  triangle. 

The  position  of  Regulus  was  determined  by  Babylo- 
nian astronomers  4,000  years  ago.  By  its  change  in 
longitude*  Hipparchus  discovered  the  precession  of  the 
equinoxes  2,000  years  ago.  Regulus  and  Denebola 
have  each  companions  of  the  eighth  magnitude,  which 

*  Longitude  is  like  right  ascension,  except  that  it  is  measured  along  the 
ecliptic,  instead  of  the  equator. 


The  Constellations  for  March  and  April.         87 

can  be  seen  with  a  powerful  field-glass.  ?  consists  of  a 
couple  of  bright  revolving  suns,  which  form  one  of 
the  finest  of  such  pairs.  C  is  a  double,  which  a  fair 
opera-glass  can  handle. 

This  asterism  is  found  in  all  the  most  ancient  repre- 
sentations of  the  zodiac  ;  the  classic  writers,  however, 
have  connected  it  with  the  story  of  the  labors  of  Her- 
cules. They  state  that  it  is  the  gigantic  lion  which  rav- 
aged the  Valley  of  Nemaea.  Hercules  having  found 
that  his  club  and  arrows  were  of  no  avail  against  this 
prodigy,  gripped  him  by  the  throat  and  strangled  him. 
King  Eurystheus  was  so  frightened,  when  Hercules 
returned  with  the  dead  lion  upon  his  shoulders,  that 
he  ordered  the  hero  thereafter  to  narrate  his  exploits 
outside  of  the  city  walls. 

Is  Regulus  as  bright  as  Procyon  ?   Of  what  color  is  Y  ?    . 

S  S  /       Queries. 

A  line  drawn  form  ?  to  e,  prolonged  5°,  meets  a  star 
of  what  magnitude  ? 

CONSTELLATIONS    FOR    APRIL. 
Bootes. 

The  later  in  the  evening  one  can  observe  Bootes,  the 
better  it  will  be  seen.  On  April  i  at  9  p.  m.  it  is  low  in  Description, 
the  northeast,  its  principal  stars  forming  a  kite-shaped 
figure  25°  in  length  (Fig.  31).  The  side  from  a  to  8  is 
lowermost,  a  is  a  star  of  the  first  magnitude,  better 
known  as  Arcturus.  A  line  from  Polaris  to  a  group  of 
three  fourth  magnitude  stars,  which  form  a  small  triangle 
5°  from  the  end  of  the  handle  of  the  Great  Dipper,  pro- 
longed an  equal  distance,  strikes  Arcturus.  A  line  from 
Polaris  to  ft  Ursae  Minoris,  the  brightest  star  in  the  bowl 
of  the  Little  Dipper,  prolonged  35°  meets  /?,  which  is  at 
the  summit  of  the  kite.  A  line  from  Polaris  to  the  star 
in  the  end  of  the  handle  of  the  Great  Dipper,  when  pro- 


88 


A  Study  of  the  Sky. 


A  double  star. 


Arcturus. 


ft 

¥ 


longed  an  equal  distance,  ends  near  Arcturus  at  a  small 
triangle  composed  of  a  third,  a  fourth,  and  a  fifth  magni- 
tude star.  These  three  stars  form  a  tail  for  the  kite. 
On  the  other  side  of  Arcturus,  at  an  equal  distance,  lies 
another  small  triangle,  likewise  composed  of  stars  of  the 

third,   fourth,    and 
fifth     magnitudes. 
These    two   trian- 
/  Y   '  gles  mark  the  feet 

/  \  of  the  bear-driver. 

w^J*  \  Arcturus  is  in  his 

i\  \  sword;  <5  and y are 

respectively  in  his 
right  and  left 
shoulders,  while  ft 
marks  his  head. 
The  little  triangle 
near  the  end  of  the 
(handle  of  the 
Great  Dipper  is  in 
his  uplifted  left 
hand. 

e  is  a  fine  double, 
as  seen  with  a  glass 
four  inches  or  more 
FIG.  3i.-BooTEs.  in    aperture;    the 

colors  of  the  components  are  golden  yellow  and  blue. 
Its  beauty  has  won  the  appellation  of  "pulcherrima." 
Over  1,200  years  are  occupied  by  one  revolution. 

Arcturus  is  a  star  of  amazing  magnitude.  So  far  is  it 
away  that  it  is  impossible  to  measure  its  distance  with 
any  sort  of  accuracy.  One  of  the  latest  measures  makes 
its  distance  1,000  million  million  miles.  From  this 
is  derived  an  estimate  that  it  is  a  million  times  as  large 


The  Constellations  for  March  and  April.          89 

as  the  sun.  Its  diameter  is  then  100  times  that  of  the 
sun.  The  reason  for  this  is  readily  grasped  by  consider- 
ing two  cubes,  one  of  which  has  each  edge  a  foot  long, 
while  each  edge  of  the  other  is  100  feet  in  length.  The 
second  cube  is  100  times  as  long,  100  times  as  broad, 
and  100  times  as  thick  as  the  first.  Therefore  it  is 
100  x  100  x  100  times  as  great  in  volume.  Arcturus  is 
approaching  us  at  the  rate  of  five  miles  a  second,  but 
this  is  only  one  component  of  its  motion.  It  moves 
along  the  face  of  the  sky  at  the  rate  of  300  miles  a 
second,  if  the  preceding  assumption  about  its  distance  is 
correct. 

The  mythological  story  usually  accepted  is  that  this 
constellation  represents  Areas,  the  son  of  Callisto. 
When  his  mother  was  changed  into  a  bear  (Ursa  Major) 
Areas,  not  recognizing  her,  was  about  to  slay  her  in  the 
chase,  when  Jupiter  prevented  so  unfortunate  a  deed  by 
taking  them  both  to  the  sky.  The  name  Bootes  is  used 
by  Homer,  and  signifies  "a  plowman."  The  Great 
Dipper  has  been  often  called  a  plow,  though  Homer 
calls  it  a  wagon.  It  seems  likely  that  Homer  regarded 
Bootes  as  being  either  the  driver  of  the  wagon,  or  the 
guide  of  the  plow. 

What  is  the  color  of  Arcturus  ?  What  is  the  color  of 
£  ?  Does  Arcturus  rise  north  of  the  east  point  of  the 
horizon,  or  south  of  it? 

Coma    Berenices. 
Only  two  stars  in  this  little  group  are  as  bright  as  the 

,  ,  ,  ~,  Description. 

fourth  magnitude.  There  are  sixteen  stars  of  the  fifth 
magnitude,  and  about  seventy-five  fainter  stars,  which 
can  be  seen  with  the  naked  eye.  All  these  lie  between 
the  large  triangle  in  the  haunches  of  Leo  and  the  kite 
in  Bootes.  The  constellation  contains  many  small  neb- 


A  Study  of  the  Sky. 


ulae,  but  a  large  telescope  is  required  to  show  them  well. 
The  most  crowded  part  of  Coma  is  a  pretty  sight  in  an 
opera-glass. 

History.  Berenice  is  an  historic  personage,  the  wife  of  Ptolemy 

III.  When  her  husband  went  to  war  against  the 
Syrians,  she  vowed  to  sacrifice  her  beautiful  hair,  in  case 
he  returned  safely.  The  sacrifice  was  made,  and  the 
Alexandrine  astronomer  Conon  commemorated  it  by 
establishing  this  constellation. 

Virgo. 
This  constellation  lies  south  of  Coma  Berenices  and 


•,- 


* 


Description. 


Spica. 


FIG.  32.— VIRGO. 

Bootes,  and  east  of  Leo.  The  principal  stars  can  be  so 
connected  as  to  form  an  outline  of  the  flowing  robe  of  a 
virgin  (Fig.  32).  She  is  in  a  recumbent  posture,  lying 
nearly  along  the  equator,  her  head  being  just  south  of  /? 
Leonis.  «,  a  star  of  the  first  magnitude,  has  the  proper 
name  Spica,  and  forms  an  equilateral  triangle  with  Arc- 
turus  and  ft  Leonis.  The  right  arm  of  the  Virgin  is 
extended  to  e,  and  the  left  hand  reaches  down  to  grasp 
a  spike  of  wheat  at  Spica.  The  celestial  equator  runs 
through  the  stars  C  and  >?  on  opposite  sides  of  her  body. 
Spica  is  very  remarkable  in  that  it  consists  of  two  re- 
volving bodies  which  occupy  but  four  days  in  one  revo- 


The   Constellations  for  March  and  April.          91 

lution.  It  has  never  been  seen  double,  but  the  periodic 
shiftings  of  the  lines  in  its  spectrum  have  shown  its 
duplicity. 

Y  is  a  fine  double,  composed  of  two  equal  suns.  It  is 
now  resolvable  without  difficulty  by  a  three-inch  tele- 
scope. The  period  of  revolution  is  175  years,  a  little 
more  than  that  of  Neptune  about  the  sun. 

Between  Coma  and  the  upper  half  of  the  Virgin's  body 
is  a  remarkable  region,  which  is  thickly  sown  with  nebulae. 

In  the  Golden  Age,  when  the  gods  dwelt  upon  the   Mythology-, 
earth,  Astraea  was  a  divinity  whom  men  especially  rev- 
erenced for  her  pure  life  and  kindly  deeds.     She  was 
the  last  of  the  immortals  to  leave  the  earth  at  the  close 
of  the  Golden  Age. 

Does  Spica  rise  south  of  the  east  point  of  the  horizon,    Queries. 
or  north  of  it  ?     Does  a  line  from  Spica  to  Polaris  pass 
through  the  handle  of  the  Great  Dipper  ?     How  many 
degrees  from  d  to  Y  at  the  Virgin's  girdle  ? 

Corvus. 

Corvus,  the  Crow,  is  further  south  than  Virgo,  and   Description 
may  be  seen  in  the  southeast  at  8 
p.  m.,  any  evening  in  April.     The 
four  brightest  stars  form  an  easily          '  \y 

recognized  quadrilateral  (Fig.  33),         i  V 

the  eastern  side  of  which  is  7°  in        '  \ 

length.      A    line    from    i    Virginis       /  \ 

through    Spica,     prolonged    west- 
ward  15°,  passes  through  the  two 
stars    in  the  northern   side   of  the 
quadrilateral.     «,  the  lowest  star  in 
the  diagram,  is  in  the  beak  of  the        FlG'  33.-CoRvus. 
Crow,  which  stands  upon  the  body  of  Hydra  (yet  to 
be  described),  pecking  at  it. 


92 


A  Study  of  the  Sky. 


Mythology, 


Queries. 


Description. 


A  temporary 
star. 


Mythology. 


Description. 


Corvus  was  Coronis,  a  mortal  princess,  who  was 
transformed  into  a  crow  by  Minerva. 

What  is  the  color  of  /?  ?  Which  star  is  the  brightest 
of  the  group  ?  How  far  from  d  is  the  nearest  visible 
star? 

Corona   Borealis. 

The  Northern  Crown  is  a  very  satisfactory  group,  be- 
cause the  eye  at  once  recognizes  a  similarity  to  the  ob- 
ject which  it  is  supposed  to  represent  (Fig.  34).  The 

constellation  is  just  east 
'#  of  the  middle  of  the 
kite  in  Bootes.  At  the 
end  of  April  it  does  not 
Across  the  meridian  till  i 
a.  m.  It  is,  at  that  time 
in  the  month,  well  up  in 
the  northeastern  sky  at 
9  p.  m.  «,  also  called 
Alphecca  or  Gemma,  is 
10°  east  of  £  Bootis. 
i  °  south  of  £  is  situated  T  Coronae,  one  of  the  small 
number  of  temporary  stars.  In  May,  1866,  it  blazed 
forth  suddenly,  equalling  Alphecca  in  magnitude. 
After  it  was  discovered  it  declined  in  brightness,  and 
had  sunk  below  the  eighth  magnitude  by  the  end  of  the 
month.  An  opera-glass  now  shows  it  as  a  star  of  the 
ninth  magnitude. 

The  crown  belongs  to  Ariadne,  whom  Bacchus  made 
his  wife.  He  gave  it  to  her  at  the  time  of  the  marriage, 
and  afterward  placed  it  among  the  stars. 

Hydra. 

Hydra  is  an  immense  snake,  whose  head  is  just  -south 
of  the  \  in  Cancer  ;  the  end  of  its  tail  is  south  of  the 


FIG.  34.— CORONA  BOREALIS. 


The   Constellations  for  March  and  April.          93 


feet  of  Virgo.  «,  also  called  Cor  Hydrse,  is  in  its  heart 
(Fig.  35).  A  line  from  Polaris  running  in  front  of  the 
sickle  in  Leo  (being  4°  away  from  e  Leonis,  which  is  at 
the  point  of  the  sickle-blade),  when  prolonged  to  a 
point  25°  distant  from  «  Leonis,  meets  Cor  Hydrse. 
From  Cor  the  snake's  body  winds  eastward  and  south- 
ward, passing  immediately  beneath  Corvus,  and  stretch- 
ing 30°  eastward  to  a  group  of  small  stars,  which  lies 
20°  south  of  p-  Virginis.  A  line  from  d  Corvi  to  e  Corvi 
prolonged  13°  meets  £. 

Chinese  astronomers  are  said  to  have  particularly  ob-   Cor  H  drse 
served  Cor  Hydrse  over  4,000  years  ago.    Their  records 


FIG.  35.— HYDRA. 

show  that  in  the  reign  of  the  emperor  Tao  it  crossed  the 
meridian  at  sunset,  at  the  time  of  the  vernal  equinox 
(March  20  in  the  modern  calendar). 

e  is  a  fine   double  for  a  three-inch    telescope  ;    one 
component  is  yellow,  the  other  blue. 

Hercules  was  sent  to  kill  a  monster  which  was  ravaging  Mythology, 
the  country  of  Lerna,  near  Argos,  and  which  has  been 
called  the  Lernean  hydra.     It  had  nine  heads,  one  of 
which  was  immortal.     Whenever  Hercules  struck  off  a 
mortal  head  with  his  club,  two  others  grew  out  to  take 


94  A  Study  of  the  Sky. 

its  place.  He  finally  burned  the  mortal  heads,  and 
buried  the  immortal  one  under  a  rock.  As  is  fitting, 
we  find  the  immortal  head  in  the  sky,  close  by  Cancer, 
the  Crab,  which  assisted  Hydra  in  the  fight  and  suc- 
ceeded in  wounding  Hercules. 

What  is  the  color  of  Cor  Hydrae?  A  line  from  e 
Corvi  to  /5  Corvi,  prolonged  eastward  10°,  strikes  what 
star  in  Hydra  ?  At  the  end  of  the  tail  of  Hydra  are  two 
fifth  magnitude  stars  3°  apart  ;  how  many  faint  stars 
can  be  seen  between  them  ? 


CHAPTER  VI. 

THE  CONSTELLATIONS  FOR  MAY  AND  JUNE. 

"Awake,  my  soul, 

And  meditate  the  wonder  !     Countless  suns 
Blaze  round  thee,  leading  forth  their  countless  worlds." 

—  Ware. 
Lyra. 
ONE  who  looks  for  this  constellation  early  in  May 

Description. 

should  observe  it  as  late  in  the  evening  as  is  convenient. 
At  9  p.  m.  it  is  in  the  northeast,  not  very  high  up.  It 
will  probably  be  recognized  at  once  because  of  the  bril- 
liancy of  Vega,  its  lead- 
ing  star  (Fig.  36).  The 
parallelogram  formed  by 
/?,  r,  d,  and  C  will  be  be- 
low  and  at  the  right  of 
Vega.  The  distance  from  * 
Vega  to  /5  is  only  8°.  /  / 

Vega  is  nearly  equidistant  /  ' 

from  Polaris  and  the  star  '  , 

at  the  end  of  the  tail  of  y*^fa. 
the    Great     Bear,    being 
over  40°  from  each.  FlG-  ^.- 

Vega  is  one  of  the  most  beautiful,  as  well  as  one  of 
the  brightest  stars.  It  is  120  millions  of  millions  of 
miles  from  us,  and  thirty  times  as  bright  as  the  sun. 
Light  consumes  twenty  years  in  coming  to  us  from  it. 
It  is  approaching  us  at  the  rate  of  ten  miles  a  second. 
It  will  be  the  pole-star  12,000  years  hence. 

e  is  one  of  the  most  famous  of  multiple  stars.     .An 

95 


96 


A  Study  of  the  Sky. 


A  variable. 


An  elliptical 
nebula. 


Mythology. 


average  eye  perceives  that  it  is  oblong,  and  a  good  eye 
Epsiion  Lyrae.  splits  it  into  two.  With  a  three- inch  telescope  each  of 
the  stars  is  again  divided  into  two  components.  Both 
pairs  revolve,  one  in  a  period  of  2,000  years,  the  other 
in  1,000  years. 

ft  is  a.  variable  star,  which  changes  from  magnitude 
3.3  to  4.5,  being  alternately  brighter  and  fainter  than  f. 
Its  period  is  nearly  thirteen  days.  There  are  curious 
anomalies  in  its  changes,  for  which  astronomers  have  yet 
found  no  reasonable  explanation. 

The  only  elliptical  nebula  which  a  small  telescope  will 
show  is  one  third  of  the  way  from  ft  to  Y-  In  a  large 
telescope  it  is  an  exceedingly  beautiful  object.  Were 
the  sun  in  the  center  of  it,  the  planet  Neptune  would  not 
lie  outside  of  it. 

Lyra  is  the  golden  harp  given  by  Apollo  to  Orpheus  : 
not  only  wild  beasts  were  charmed  by  its  sweet  strains, 
but  even  trees  and  rocks,  which  moved  from  their  places 
to  follow  the  harper.  With  it  Orpheus  descended  to 
Hades,  stopped  the  sound  of  torment  by  its  music,  and 
won  back  his  dead  wife,  melting  stern  Pluto's  heart. 

Is  8  double  to  ,the  naked  eye  ?  What  is  the  color  of 
Vega  ?  Is  Vega  above  the  horizon  more  or  less  than 
twelve  consecutive  hours  ? 

Hercules. 

A  large  part  of  Hercules  lies  between  Lyra  and  Co- 
Description,  rona  Borealis.  It  therefore  appears  to  be  above  Lyra 
when  seen  low  in  the  east.  During  May  a  better  view 
of  it  can  be  obtained  after  9  p.  m.  than  before  that  hour. 
The  giant  is  represented  with  his  head  toward  the 
equator  and  his  feet  toward  the  north  pole  (Fig.  37). 
a  is  in  the  head  ;  the  shoulders  are  marked  by  ft  and  3  ; 
e  and  C  are  in  the  belt.  The  positions  of  the  limbs 


Queries. 


The  Constellations  for  May  and  June.  97 

are  indicated  by  dotted  lines  in  the  diagram.  The 
entire  length  of  the  figure  from  a  in  the  head  to  T  in  the 
right  foot  is  35°.  «  is  nearly  30°  from  both  «  Lyrae 
and  «  Coronse.  /?  is  nearly  half  way  from  a  to  a 
Coronae.  The  extremity  of  the  left  arm  is  marked  by 
a  small  group  less  than  two  thirds  of  the  way  from  a  to 
a  Lyrae. 

a  is  a  fine  double  star,  which  a  two-inch  telescope  can   A  fine  double, 
resolve  ;  the  companion  is  blue. 

One  third  of  the  way  from  in  to  C  is  the  finest  globular  The  great 

globular 

cluster  in  the  northern  ^  cluster, 

hemisphere.     It  is  vis- 
ible to  the  naked  eye  w6  J^-f 
on  a  dark  night.    With 

a  small  telescope  it  *y/ 

looks   like    a    nebula.  ±^v 

A  large  glass  resolves  •      * ,  Wf 

it  into  thousands  of  ^^'' ''  \ 

small  stars,  which  are         -y  ,'  ^ 

crowded  together  into  ^-%  ,  ;  \  Q 

one   glowing   mass   in  °        ^t     ~*^t-— -«rf  -j*. 

the  center,  from  which  ,  /      y^ 

streams     radiate    out- 
ward like  the  arms  of  / 
a  star-fish.     When  one                                   \   / 
reflects  that  each  star                                  ^a 
is  a  sun,  and  that  the                 FlG-  ST.-HERCULBS. 
distance  of  the  cluster  from  us  is  so  amazing  that  astron- 
omers have  not  been  able  to   measure  it,   or  even   to 
discover  any  changes  in  the  relative  positions  of  the  stars 
due  to  their  mutual  attractions,  the  grandeur  of  the  sys- 
tem fairly  appals  the  imagination. 

The  region  of  the  heavens  in  which  Hercules  lies  is  of  Qur  goal 
special  interest,  because  several  astronomers  have  shown 


98 


A  Study  of  the  Sky. 


Mythology. 


Queries. 


Description. 


that  the  sun  with  his  attendant  planets  is  moving  in  that 
direction. 

Hercules  is  the  giant  whose  marvelous  strength  was 
celebrated  so  often  in  Greek  legends.  The  most  famous 
of  his  exploits  were  the  twelve  labors,  which  he  per- 
formed at  the  bidding  of  Eurystheus.  The  constella- 
tions of  Leo,  Draco,  Hydra,  and  Scorpio  are  all  con- 
nected with  the  stories  of  these  exploits,  which  may  be 
found  in  detail  in  a  classical  dictionary. 

What  is  the  color  of  «  ?  What  is  the  appearance  of 
the  great  globular  cluster  to  the  naked  eye  on  a  moon- 
less night  ?  Toward  what  star  in  Corona  does  the  belt 
point  ? 

Cygnus. 

Cygnus  lies  east  of  Lyra  ;  it  is  often  called  the 
Northern  Cross,  because  the  chief  stars  form  an  excellent 
Roman  cross  (Fig.  38).  When  seen  low  in  the  east  the 

cross  appears  to 

lie    on   its   side ; 

the  upright  piece 

•  is  over  20°  long, 

_-_  ypj  and  extends  from 

fl  \         /  «,    also   called 

JW'  Deneb,   to  /?,    or 

,'VX,  Albireo.      The 

^~;f  cross-piece    runs 

W-  \ 

..'Ye  \  from  d toe.  The 

-^- _^'  *  x  bill  of  the  Swan  is 

T $  at  /5,  and  the  out- 

FIG.  38-CYGNus.  stretched  wings 

are  shown  by  the  dotted  line  from  K  to  /JL.  ?,  at  the  in- 
tersection of  the  upright  and  cross-piece,  is  18°  east  of  « 
Lyrse,  and  a  little  nearer  to  Polaris.  A  line  from  /? 
Lyrse  to  ?  Lyrae,  prolonged  8°,  reaches  /?.  The  cross  lies 


The   Constellations  for  May  and  June.  99 

in  a  portion  of  the  Milky  Way  which  is   rich  in   fields 

fine  for  an  opera-glass.     Some  of  the  finest  regions  are   Fine  fields. 

within  a  few  degrees  of  a  •  they  appear  to  the  unaided 

eye  simply  as  bright  portions  of  the  Galaxy.     There  are 

also  some  dark  rifts  near  by,  which  strikingly  contrast 

with  the  glories  all  about  them. 

/?  is,  for  a  small  telescope,  the  finest  colored  double  in  A  colored 
the  sky.     A  magnifying  power  of  ten  diameters  splits  it  double- 
with  ease.     With  larger  telescopes  the  contrasted  colors 
are  seen  finely  by  throwing  the  stars  out  of  focus. 

6 1  is  a  star  of  magnitude  5.5,  which  is  noted  as  the 
first  star  whose  distance  was  measured.  It  is  over  500,- 
ooo  times  as  far  away  as  the  sun  ;  only  two  stars  are 
known  to  be  nearer.  61  is  6°  from  e,  and  forms  a  par- 
allelogram with  «,  y,  and  £. 

A  little  less  than  one  third  of  the  way  from  a  to  fc,  one 
degree  north  of  the  fourth  magnitude  star  o  *,  is  o 2, 
which  an  opera-glass  shows  as  a  triple  lying  in  a  pretty 
field  of  smaller  stars. 

The  Latin  poet  Ovid  states  that  Cygnus  was  a  friend  M^holo 
of  Phaeton,  the  unhappy  youth  with  whom  the  horses  of 
the  sun  ran  away.     The  friend' s  grief  was  so  poignant 
that  Jupiter  changed  him  to  a  swan. 

A  line  from  a  to  a  Lyrae,  prolonged  an  equal  distance, 
meets  what  star  in  Hercules  ?  A  line  from  /?  to  a  Lyrae, 
prolonged  13°,  meets  what  star  in  Hercules?  A  line 
from  Y  to  «  Lyrae  points  to  what  bright  star  in  Hercules  ? 

Draco. 

The  head  of  the  Dragon  is  marked  by  a  conspicuous 
quadrilateral  formed  of  /?,  y,  £,  and  \>  (Fig.  39).  It  lies 
just  north  of  £  Herculis,  which  is  the  giant's  left  foot. 
The  distance  from  7-  to  £  is  5°.  y  forms  an  equilateral  tri- 
angle with  Polaris  and  the  star  at  the  end  of  the  handle 


loo  A  Study  of  the  Sky. 

of  the  Great  Dipper.  The  convolutions  of  the  Dragon's 
form  can  be  best  learned  from  the  diagram,  with  the  help 
of  the  following  data.  The  first  fourth  of  the  body  lies 
between  Lyra  and  the  pole,  e,  where  the  body  is  coiled 
and  turns  sharply,  is  nearly  half  way  from  Polaris  to  3 
+-7>o/Qr,s  Cygni.  «  may  be 

A>^    found  by  prolonging 
a   line  from  Polaris 
Kf        to  f  Ursae    Minoris 

r  13°.     A,  at  the  end 

I          of  the  Dragon's  tail, 
a*"        ^es  between  Polaris 
and  the  bowl  of  the 
y^  i'  Great    Dipper,   and 

X 


jfi^        ^  ^^  Majoris.      «,   which 

/  "^_<  is   about    half    way 

J    ^  between    C    Ursae 

FIG.  39-DRAco.  Majoris   (Mizar) 

and  Y  Ursae  Minoris, 

was  the  pole-star  5,000  years  ago.     Its  brightness  has 
probably  diminished  much  during  the  past  two  centuries. 
It  was  previously  rated  as  of  the  second  magnitude. 
Mythoio  There  are  two  mythological  stories  with  which  this 

constellation  is  associated.  The  Thracian  hero  Cadmus 
slew  a  dragon  which  guarded  a  well  from  which  he 
wished  water.  Minerva  advised  him  to  sow  the  dragon's 
teeth  ;  armed  men  sprang  up  from  them.  Another 
dragon,  Ladon  by  name,  who  guarded  the  golden 
apples  of  the  Hesperides,  was  slain  by  Hercules  and 
placed  among  the  stars. 

Sagitta. 

Sagitta,  the  Arrow  (Fig.  40),   is  a  neat  little  figure, 
Description.        which  lies  south  of  Cygnus.     «  and  /?  mark  the  butt  of 


The   Constellations  for  May  and  June.  i  o  i 

the  arrow,  and  Y  is  at  its  point  ;  the  length  of  the  arrow 
is  7°.  A  line  from  «  Lyrse  to  ft  Cygni,  prolonged  11°, 
meets  ^,  and  is  nearly  perpendicular  to  the  arrow.  The 
constellation,  though  small,  offers  a  fine  field  for  a  small 
telescope.  * 

Two  degrees  southwest  of  the  butt  of  the  arrow  lies  e,    pieasing 
of  the  sixth  magnitude,  which  is  a  pretty  pair  in  a  good   obJects- 
opera-glass.     Less  than    2°    beyond   the   point    of   the 
arrow    a   small   telescope 
will  pick  up  a  pretty  triple  _ 

star,  0.       Four  degrees  ^**-«.  ^0 

from  the  butt  of  the 
arrow,  toward  the  belt  of 
Hercules,  lies  a  cluster  FIG. 

visible  with  an  opera-glass.  A  yellowish  star  of  the 
sixth  magnitude,  2^°  south  of  ~f,  is  the  brightest  of  a 
group  which  shows  nicely  in  an  opera-glass,  and  con- 
tains a  red  star. 

Scorpio. 

In  the  latter  part  of  May  Scorpio  is  on  the  meridian 

*\  J  r  Description. 

in  the  south  at  midnight.  The  later  in  the  evening  one 
looks  for  it  the  better,  for  though  many  of  the  stars  are 
very  bright,  the  constellation  being  the  most  brilliant  in 
the  zodiac,  they  never  get  high  in  the  heavens.  The 
brightest  star,  «,  is  Antares  (Fig.  41),  and  maybe  found 
by  prolonging  a  line  from  Polaris  to  ft  Herculis,  the  pro- 
longation being  two  thirds  as  long  as  the  original  line. 
The  curve,  composed  of  /9,  3,  and  TT,  is  7°  in  length,  and 
resembles  the  blade  of  a  scythe,  the  snath  of  which 
extends  down  to  e  •  Antares  is  at  one  of  the  handles. 
Below  e  the  curve  is  U-shaped,  and  ends  at  the  bright 
pair  A  and  o,  which  lie  in  the  Milky  Way  and  mark  the 
animal's  sting.  The  sting  is  17°  southeast  of  Antares. 
The  distance  from  Antares  to  ft  is  9°. 


102 


A  Study  of  the  Sky. 


Antares. 


A  rich  cluster. 


Mythology. 


Antares  is  a  magnificent  double,  having  a  greenish 
companion  fairly  within  the  blazing  aureole  about  the 
principal  star.  This  was  discovered  in  a  curious  way. 
Ordinarily  a  small  telescope  will  not  show  the  com- 
panion, because  of* the  overpowering  brilliancy  of  the 
large  star.  But  on  one  occasion  in  1819,  when  the  star 
was  emerging  from  behind  the  moon,  the  small  star 

popped  out  first,  and 
was  seen  for  an  in- 
stant before  the  large 
one  appeared. 

/3  is  a  fine  double 
for  a  two-inch  tele- 
scope, v  is  2°  east  of 
/?,  and  is  much  easier 
to  split  than  ft.  A 
large  telescope  di- 
vides each  compo- 
nent of  v  again,  mak- 
ing ita  quadruple  star. 
Half  way  between  Antares  and  /?  lies  a  cluster,  which 
Herschel  described  as  the  richest  and  most  condensed 
mass  of  stars  in  the  firmament.  It  is  visible  with  a  small 
telescope,  but  a  large  one  is  needed  to  bring  out  its 
beauty.  In  May,  1862,  a  star  blazed  out,  apparently 
in  the  center  of  the  cluster,  almost  extinguishing  the 
latter  by  its  brightness  ;  in  less  than  a  month  it  faded 
into  invisibility. 

One  of  the  mythological  stories  connects  a  scorpion 
with  the  story  of  Orion,  stating  that  the  mighty  hunter 
boasted  that  he  would  kill  all  the  wild  beasts  on  the 
earth,  whereupon  the  earth  sent  forth  a  scorpion  which 
stung  and  killed  him.  When  ^sculapius  attempted  to 
bring  him  back  to  life,  Jupiter,  knowing  that  Orion  had 


I* 


FIG.  41.— SCORPIO. 


The  Constellations  for  May  and  June.  103 

already   experienced   his    full   share   of    life's   sorrows, 
smote  the  physician  with  a  thunderbolt. 

What  is  the  color  of  Antares  ?    Which  is  the  brighter,    Queries 
ft  or  <5?     At   about   what   point   of    the   horizon   does 
Antares  set  ?     Is  Antares  above  the  horizon  twelve  con- 
secutive hours,  or  fewer  ? 

THE    CONSTELLATIONS    FOR   JUNE. 

Libra. 

The  principal  stars  of  this  constellation  form  a  rude  Description, 
square  (Fig.  42),  which  lies  half  way  between  the  feet  of 
Virgo  and  the  scythe-blade  in  Scorpio.     The  distance 
from  «  to   ft  is   9°.     a,   which   lies  on  a   line  from  ft 
Scorpii   to    a    Virginis, 
appears  elongated  to  a 
keen  eye;   it  falls  an 
easy  prey  to  an  opera- 
glass.     Near  the  middle 
point  of  a  line  joining  ft 
to  jj.  Virginis  is  d,  a  star 

of  the  fifth  magnitude,  /  xx 

which  is  a  very  remark-  /  ^ 

able  variable.       In   five  ^^  NN 

and  a  half  hours  it  sinks     r\  ^  \ 

\  \ 

to  the  sixth  magnitude ;  Nx  *& Cl 

six    and    a    half    hours  \ 

afterward  it  has  regained  \ 

its  former  brightness, 


and  remains  in  that  es- 
tate for  forty-four  hours,  FlG-  42.— LIBRA. 
after  which  it  fades  again.      Its  entire  period  is  fifty-six 
hours. 

Libra  was  originally  a  part  of  Scorpio,  forming  the  History, 
claws  of   that  venomous   animal.     The    Egyptians   are 


104 


A  Study  of  the  Sky. 


Queries. 


Description. 


A  fish  story. 


said  to  have  formed  it  into  a  separate  constellation  as 
early  as  300  B.  C.  In  the  time  of  Augustus  Caesar  it 
was  regarded  as  the  balance  belonging  to  Virgo,  the 
goddess  of  justice. 

What  is  the  color  of  /?  ?  Where  are  sixth  magnitude 
stars  more  thickly  sown,  northeast  or  southeast  of  the 
1 '  square "  ?  A  line  from  Y  to  Polaris  passes  through 
what  small  but  plain  constellation  ? 

Delphinus. 

A  line  from  Polaris  through  a  Cygni,  prolonged  30°, 
ends  at  a  small  diamond-shaped  figure  (Fig.  43),  which 
contains  three  stars  of  the  fourth  magnitude  and  one  of 
the  third.  The  length  of  the  dia- 
mond from  ft  to  Y  is  2^2°.  In- 
cluding e  we  have  a  wedge-shaped 
figure  which  has  been  called 
4 'Job's  Coffin." 

Y  has  a  bluish  companion  of  the 
sixth  magnitude,  which  a  two-inch 
telescope  will  show. 

The  dolphin  is  supposed  to  be 
the  fish  upon  whose  back  Arion, 
the  ancient  bard  and  musician, 
took  his  celebrated  ride.  When 
he  was  returning  to  Corinth  from  Sicily,  where  he  had 
won  a  prize  in  a  musical  contest,  the  treasures  which 
had  been  presented  to  him  roused  the  cupidity  of  the 
sailors,  who  planned  his  murder.  Obtaining  their  per- 
mission to  play  the  cithara  once  more,  he  charmed  a 
school  of  dolphins  by  his  melodies  ;  he  then  leaped  into 
the  sea,  and  was  brought  safely  to  land  by  one  of  them. 

Aquila. 
This  constellation  lies  just  south  of  Sagitta,  and  rises 


\ 


FIG.  43.— DELPHINUS. 


The  Constellations  for  May  and  June.  105 

near  the  east  point  of  the  horizon  ;  in  the  middle  of  June 
it  is  on  the  meridian  at  2  a.   m.     It  will  therefore  be  Description, 
best  not  to  look  for  it  before  9  p.  m.     Altair,  its  prin- 
cipal star,  may  be  located  by  a  line  from  Polaris  through 
^Cygni;  it  is  flanked  '•'^ 

by  the  stars  /?  and  Y  ^      \ 

(Fig.    44),    which    -^"'•a      \^ 
form  with   it  a  line          -i-£  x 

5°    long,    running  /  \ 

athwart  the  Galaxy.          '  ^ 

This  line  prolonged       /  \ 

south  ward  8°  strikes      /        ^^  \ 

6.     The  rest  of  the  e^  -  '  *  "^  ^  \ 

figure,  which  bears  ^  "* "  *•  ^  ^\* 

not  the  remotest  re-  ~^ 

semblance   to    an  • 

eagle,  is  easily  found  FlG"  44.-AQuiLA. 

by  the  help  of  the  diagram.  Altair  is  a  million  times  as 
far  from  us  as  the  sun,  its  light  taking  sixteen  years  to 
reach  us.  rh  which  is  8°  south  of  Altair,  is  a  well-known 
variable,  having  a  period  of  seven  days  and  a  fraction,  in 
which  it  loses  and  regains  over  a  magnitude.  Its  vari- 
ations can  be  well  seen  by  comparing  it  for  a  few  nights 
with  0  and  f,  which  are  near  by. 

Aquila  is,  according  to  one  account,  the  eagle  of  Ju- 

...  j  i        i  •       i  •       ,          Mythology. 

piter,  which  stood  by  his  throne.  Another  story  is  that 
Merops,  a  king  of  the  island  of  Cos,  attempted  suicide, 
wishing  to  follow  his  wife  to  the  under  world.  Juno's 
proverbial  kindness  of  heart  led  her  to  thwart  this  wish, 
by  placing  him  among  the  stars,  in  the  form  of  an  eagle. 
The  line  of  three  stars,  in  which  Altair  lies,  when  pro- 
longed northward,  passes  through  what  brilliant  star? 
What  is  the  color  of  Altair?  Does  a  line  from  A  to 
Polaris  pass  through  a  Lyrae  ? 


Description. 


io6 


A  Study  of  the  Sky. 


Serpens  and  Ophiuchus. 

We  treat  these  constellations  together,  since  they  form 
the  one  figure  of  a  man  grasping  a  serpent  (Fig.  45). 
Ophiuchus,  the  serpent-bearer,  is  between  Hercules  and 
Scorpio.  The  head  of  the  serpent  is  marked  by  the 
triangle  formed  of  ft,  f,  and  #,  in  the  upper  right  hand 
corner  of  the  diagram  ;  it  lies  10°  south  of  Corona. 


The  serpent 
turns. 


FIG.  45. — SERPENS  AND  OPHIUCHUS. 

Thence  the  body  of  the  serpent  runs  southward  through 
«  and  e  Serpentis  to  d  and  e  Ophiuchi,  where  one 
hand  of  Ophiuchus  grasps  the  snake.  The  next  two 
stars  in  it  are  C  and  ^  Ophiuchi.  The  distance  from 
«  Serpentis  to  C  Ophiuchi  is  22°.  These  two  stars  form 
with  A  Ophiuchi  and  IJL  Serpentis  a  fine  parallelogram. 
From  rj  Ophiuchi  the  snake's  body  goes  eastward 
and  northward,  as  shown  in  the  diagram,  ending  at  0 
Serpentis,  which  is  on  a  line  from  Polaris  to  7-  Lyrse, 


The  Constellations  for  May  and  June.          107 


prolonged  30°  further  ;  0  is  also  7°  west  of  8  Aquilse. 

«  Ophiuchi,  which  marks  the  man's  head,  can  be 
found  by  drawing  a  line  from  Polaris  to  /?  Draconis,  and 
prolonging  it  an  equal  distance.  It  may  also  be  located 
by  a  line  from  «  Bootis  to  the  head  of  the  serpent,  pro- 
longed as  far  again.  «  Herculis  is  but  6°  from  a 
Ophiuchi.  /5  and  ?  are  in  the  right  shoulder  of  Ophiu- 
chus,  i  and  fc  in  his  left.  His  right  knee  is  at  >?,  and  his 
left  at  C  ;  his  right  foot  is  at  0,  and  his  left  stands  on 
Scorpio,  close  to  a  Scorpii.  While  Serpens  is  compara- 
tively easy  to  learn,  Ophiuchus  requires  some  attention  ; 
therefore  we  have  entered  into  considerable  detail. 

One  third  of  the  way  from  0  Serpentis  to  a  Ophiuchi 
an  opera-glass  will  pick  up  a  cluster.  In  the  same  line,  clusters. 
not  far  from  «,  is  another  cluster  almost  bright  enough 
to  be  visible  to  the  naked  eye.  There  are  many  fine 
double  stars  and  clusters  in  these  constellations,  but  they 
are  chiefly  for  good-sized  telescopes. 

Ophiuchus  is  supposed  to  represent  ^Lsculapius,  the 

*j    .  '  Mythology- 

god  of  medicine.  Many  temples  were  erected  in  his 
honor  in  various  parts  of  Greece,  and  were  used  as  hos- 
pitals, as  well  as  for  worship.  Tame  serpents  were  kept 
at  Epidaurus,  the  principal  seat  of  his  worship,  and  the 
god  himself  frequently  assumed  the  form  of  a  serpent. 

Which  is  the  nearer  to  a  Herculis,  the  head  or  the 
left  shoulder  of  Ophiuchus  ?  A  small  triangle  of  stars  is  Queries. 
5°  southeast  of  /?  Ophiuchi  ;  what  are  their  magnitudes? 
Two  fifths  of  the  way  from  «  Ophiuchi  to  0,  the  last  star 
in  the  serpent's  tail,  is  a  double  star  72  Ophiuchi  ;  what 
is  its  magnitude  ? 

Sagittarius. 

This  constellation  is  next  to  Scorpio,  and  east  of  it. 

T1  -1H/-T  ••  •  1-  Description. 

In  the  middle  of  June  it  is  on  the  meridian  at  i  p.  m. 
It  is  best  therefore  not  to  study  it  till  10  p.  m.,  or  else 


io8 


A  Study  of  the  Sky. 


The  "  milk- 
dipper." 


Fine  fields. 


Description. 


to  wait  till  the  latter  part  of  July,  when  it  can  be  seen 
well  at  9  p.  m.  The  eye  at  once  perceives  the  ' '  milk- 
dipper"  (Fig.  46),  the  bowl  of  which  is  upside  down, 
and  is  defined  by  the  stars  C,  T,  <r,  and  <p  ;  A  is  in  the  end 
of  the  handle,  and  is  10°  from  C.  Sagittarius  is  a 

Centaur,  who  is 
shooting  at  the 
Scorpion.  The 
bowl  of  the  milk- 
dipper  is  in  his 
\  body.  A,  d,  and 

\     «  £    represent   the 

^ *±£  bow    on    which 

^r -W 

**  T y  there  is  an  arrow, 

'  whose  tip  is  at  f. 

In  the  latter 
part  of  August, 
when  the  constel- 
lation is  on  the 
meridian,  full  in 
the  south  at  9  p.  m.,  one  may  well  explore  the  Milky 
Way  in  and  above  Sagittarius,  with  the  help  of  an 
opera-glass  or  small  telescope.  There  are  several  fine 
clusters  and  beautiful  fields.  Their  whereabouts  are  in- 
dicated to  the  naked  eye  by  bright  spots  in  the  Galaxy. 

Cepheus. 

Cepheus  lies  between  Cassiopeia  and  Draco.  The 
five  brightest  stars  form  a  rude  square  surmounted  by  an 
isosceles  triangle  (Fig.  47).  The  entire  figure  is  20° 
long.  r  is  12°  from  Polaris,  nearly  on  a  line  from  it  to  /? 
Cassiopeiae.  «  forms  an  equilateral  triangle  with  Polaris 
and  £  Cassiopeiae.  A  line  from  f  to  «,  prolonged  an 
equal  distance,  meets  «  Cygni.  King  Cepheus  sits  behind 


FIG.  46. — SAGITTARIUS. 


The  Constellations  for  May  and  June.  109 

his  wife  Cassiopeia ;  his  head  is  marked  by  C  and  two 

fainter   stars    close   by  it  ;    his  foot-stool  is   the  tail  of 

the  Little  Bear  ;    ^  is  in    his  left 

knee  ;  the  rest  of  his  figure  may  V  iBT 

be  supplied   as    one    pleases.       d         I      \ 

is  a  variable  which  has  a  period         I        \ 

of  5^  days,  and  ranges  in  magni-  x 

tude  from  3.7  to  4.9.     A   good        {  ^fc'/9 

1  1     •        i       1  •    •  -,  ^P  &         A  variable 

spy-glass  reveals  its  duplicity ;  the  \\  double. 

two  stars  are  respectively  orange    ^^  \ , 

and  blue.     /?  is  also  a  double,  the   '<  ^  \ 

large  star  being  white,  the  small         \ 

one   blue  ;    a   two-inch   telescope  v 

handles  it  nicely.     //,  perhaps  the  ^          / 

reddest  naked-eye  star  visible  in          £  |Jf 

the  United  States,    is  located  4° 

from  C,  toward  «,  but  south  of  a        ^- 47.-cEpHEUs. 

direct   line   between    the   two.       Its   magnitude   varies 

irregularly  from  3.7  to  4.8. 

Cepheus,  like  some  men  nowadays,  was  best  known 
through  his  family.  The  "  Classical  Dictionary"  says 
sententiously  of  him,  "  King  of  Ethiopia,  son  of  Belus, 
husband  of  Cassiopeia,  and  father  of  Andromeda,  was 
placed  among  the  stars  after  his  death." 
Capricornus. 

This  constellation  is  east  of  Sagittarius.  The  line  of 
«  Aquilae  (Altair)  and  its  two  immediate  comrades,  ex-  Descripti 
tended  southward,  strikes  into  the  heart  of  it.  We  shall 
not  try  to  imagine  that  it  is  a  goat,  but  rather  the  cross- 
section  of  a  row  boat  (Fig.  48).  The  distance  across 
the  boat  from  a  to  3  is  22°.  A  line  from  Polaris  to  Y 
Cygni,  prolonged  an  equal  distance,  ends  at  «,  which 
the  naked  eye  shows  as  a  double.  An  opera-glass 
shows  ft  to  be  double.  By  noticing  that  there  is  a  pair 


i  io  A  Study  of  the  Sky. 

Pairs  of  stars.  °f  stars  at  eacn  corner  of  the  figure,  one  will  have  no 
difficulty  in  picking  out  the  outline  of  the  constellation 
in  the  heavens. 

A  good  view  of  Capricornus  cannot  be  obtained  dur- 
ing June   until  after   midnight.      In   the   latter   part    of 

a 


e  ^ 


i 

i 

i 

i 

i 
i 
i 
i 


FIG.  48.— CAPRICORNUS. 

August  it  reaches  the  meridian  before  n    o'clock,  and 
is  well  situated  for  observation  at  9  o'  clock. 

The   mythology  of   this   constellation   is    ' '  confusion 

Mythology.         worse  confounded. ' '     One  who  tries  to  study  it  up  may 

be  pardoned  for  wishing  that  Jupiter  had  given  the  goat 

a  nice  pasture  in  his  back  yard,  and  kept  it  out  of  sight 

of  mortals. 


CHAPTER  VII. 

/'  ••' 

THE    ASTRONOMER. 

"  Priest-ministrant  within  this  mighty  Fane, 
Whereon  thou  standest  now  is  holy  ground  ; 
Divinest  gift  is  thine — to  gaze  the  first 
On  glories  yet  unseen  by  mortal  eyes." 

—A.   V.   G. 

STUDENTS  of  English  literature  in  our  colleges  are 

&  An  author  and 

now  encouraged,  when  studying  the  works  of  any  his  works, 
particular  author,  to  study  the  man  as  well,  to  become 
familiar  with  his  daily  life,  to  learn  his  personal  history, 
to  study  his  habits  and  his  environment.  In  this  way 
one  is  the  better  equipped  to  understand  and  to  criticise 
his  works,  for  the  man  is  pretty  sure  to  be  reflected  in 
his  writings.  Learning  his  point  of  view,  we  can  the 
better  appreciate  the  conclusions  which  he  reaches,  and 
can  make  allowance  for  his  personal  bias.  If  he  be  a 
thoroughly  lovable  man  and  an  inspiring  writer,  we  gain 
a  greater  uplift  from  unconsciously  associating  the  man's 
character  with  his  productions. 

If  this  method  is  valuable  in  English  literature,  why 

•         «  i     •  i  -,        A  1  e  Why  not 

should   it   not   be   in    astronomy  ?     Almost   all   of   our  analyze 

,     ,  r  ,  .  .  P    astronomers  ? 

knowledge  of  astronomy  comes  trom  the  writings  of 
men  who  state  that  they  have  perceived  this  and  that, 
that  they  have  made  such  and  such  measurements,  that 
they  have  drawn  certain  conclusions.  Why  should  we 
not  inquire  into  the  characters  of  these  men  ?  If  some 
astronomer,  who  is  noted  for  his  powerful  fancy, 
announces  that  he  has  found  strong  evidence  that 


112 


A  Study  of  the  Sky. 


Specialists. 


An  astronomer 
defined. 


Jupiter  has  intelligent  inhabitants,  why  should  we  not 
discount  his  statements  because  of  the  exuberance  of 
his  imagination?  An  astronomer,  whose  work  is  the 
observation  of  comets  and  asteroids,  together  with  com- 
putation of  their  orbits,  expresses  an  opinion  on  a 
recondite  point  in  solar  physics.  Certainly  his  opinion 
should  not  have  much  weight  in  comparison  with  that  of 
a  special  student  of  the  sun.  It  may  be  that  astron- 
omers in  general  are  altogether  too  conservative,  and 
unwilling  to  welcome  a  piece  of  work  which  appears  to 

overthrow  some  re- 
ceived theory. 

No  further  illus- 
trations are  needed 
to  show  that  the 
personality  of  the 
observer  is  a  pow- 
erful factor  in  his 
scientific  utterances. 
Let  us  therefore  sub- 


ject  the  average  as- 
tronomer to  a  pretty 
thorough  analysis, 
so  that  we  may  un- 
derstand him  and 
his  work  the  better. 
Who,  then,  is  the 
astronomer  ?  Is  he 
the  long-haired  man 

FIG.  49.—  CHARLES  A.   YOUNG,   PROFESSOR  OF    who  Stands  upon  the 
NOMV  AT  PRINCETON  UNIVERSITY. 


sells  a  peep  through  his  telescope  for  ten  cents  ?  By  no 
means.  Is  he  the  wealthy  gentleman  who  is  deeply  in- 
terested in  the  science,  and  has  a  private  observatory, 


The  Astronomer.  113 

in  which  he  spends  quite  a  little  time  surveying  the 
wonders  of  the  sky  ?  Not  at  all.  Is  he  the  professor 
who  has  charge  of  an  observatory,  and  uses  its  instru- 
ments for  the  instruction  of  the  college  students  ?  Not 
usually. 

The  astronomer,  whether  in   charge  of  an  elaborate  An  original 
observatory,    filled   with  costly  instruments,    or  simply  lnvestlsator- 
the  possessor-  of  a  good  opera-glass,  or  small  portable 
telescope,  is  the  man  who  by  patient  study  of  the  sky 
adds  to  the  sum  total  of  astronomical  knowledge.     It  is 
possible  to  be  an  astronomer  if  possessed  of  no  optical 
instruments  except  a  pair  of  good  eyes,  but  the  range  of 
naked-eye    work    is  extremely   limited.     The    original 
investigator,   then,   is  the  man  to  whom  we  shall  pay 
attention. 

First  as  to  his  physique.  He  may  be  tall  or  short, 
broad  shouldered  or  slim,  thin  or  tolerably  fleshy,  but  l 
he  is  almost  always  possessed  of  a  good  constitution, 
which  will  endure  rigors  of  cold  or  extremes  of  heat,  and 
will  not  break  down  under  a  severe  pressure  of  work, 
night  and  day,  year  in  and  year  out. 

His  nervous  system  is  well  developed,   his  eyesight  HIS  nervous 
and  hearing  are  fair,  and  his  sense  of  touch  is  delicate.    system- 
His  hand  is  steady  under  trying  circumstances.     Ner- 
vousness is  not  a  bane  of  his  life,  causing  him  to  lose 
control  of  himself  at  moments  when  every  faculty  must 
be  at  its  best,  and  every  muscle  obedient  to  his  behest. 

When  observing  a  transit  of  Venus,  a  repetition  of 

.  M1  .          «•'«•*.  i        •  Self-control. 

which  will  not  occur  during  his  lifetime,  he  is,  at  the 
critical  instants,  as  cool  and  collected  as  if  sitting  in  his 
office,  looking  over  a  new  book.  This  self-control 
comes  from  long  training  ;  it  finds  a  parallel  in  the 
steadiness  with  which  a  surgeon's  hand,  though  pre- 
viously trembling,  executes  the  crucial  part  of  a  difficult 


A  Study  of  the  Sky. 


Night  work. 


Education. 


operation,  when  the  life  of  the  patient  hangs  in  the  bal- 
ance. This  ability  to  exercise  self-control  is  enhanced 
by  the  astronomer's  plain  living  and  regular  habits. 

It  is  a  mistake  to  suppose  that  he  is  ordinarily  at  work 
at  all  hours  of  the  night,  and  tucks  in  bits  of  sleep  partly 

by  day  and  partly 
by  night,  under  the 
direction  of  an  alarm 
clock.  For  the 
majority  of  nights 
are  cloudy,  so  that 
no  observing  is 
done ;  when  the 
weather  is  clear 
he  usually  has  on 
hand  some  work 
which  comes  during 
a  certain  portion  of 
the  night.  He  rarely 
works  all  night. 
Comet  hunters  are 
exceptions  in  the 


FIG.  50.— EDWARD   S.    HOLDEN,  DIRECTOR   OF 
THE  LICK  OBSERVATORY. 


matter  of  regular- 
ity. They  change  their  times  of  observing  from  night 
to  night,  working  generally  during  those  hours  when  the 
moon  is  below  the  horizon  ;  the  faint  objects  which  they 
discover  are  not  commonly  readily  visible  in  moonlight. 
Astronomers  are,  on  the  whole,  well-educated  men, 
especially  those  who  are  the  directors  of  large  observa- 
tories. Very  little  can  be  done  in  their  science  without 
a  sound  knowledge  of  elementary  mathematics.  The 
principles  of  physics  and  mechanics  come  up  continually. 
An  American  astronomer  who  cannot  read  scientific 
German  and  French  with  considerable  ease  is  often 


The  Astronomer. 


seriously  hampered  in  his  work  ;  for  he  must  master  the 
contents  of  many  publications  in  those  languages.  Often 
he  wishes  to  read  Italian  ;  a  knowledge  of  Latin  and 
Greek  is  not  infrequently  of  service. 

An  astronomer  may  be  very  narrow-minded.  The 
ceaseless  round  of  computation  by  day  and  observation 
by  night,  demanding  every  iota  of  his  time,  has  a  strong 
tendency  to  keep  his  mind  from  expanding  along  any 
other  lines.  But  if, 
as  usual,  he  has 
been  through  an 
old-fashioned,  now 
much  berated,  col- 
lege curriculum,  the 
liberalizing  effect  of 
the  four  years  of 
study  of  various 
branches  of  knowl- 
edge keeps  him 
from  undue  narrow- 
ness. It  is  note- 
worthy that  men  of 
only  moderate  men- 
tal caliber  are  the 
most  likely  to 
shrivel  up.  The 
mental  giants  have 
a  many-sidedness, 
which  leads  them  to  explore  other  realms  of  knowledge 
to  a  moderate  extent.  One  of  the  best  text-books  on 
political  economy  published  in  this  country  is  the  work 
of  an  astronomer,  most  of  whose  time  is  occupied  with 
directing  intricate  calculations  belonging  to  the  strictly 
mathematical  side  of  the  science. 


FIG.  51.— SIMON    NEWCOMB,    SUPERINTENDENT 
OF  THE  "  NAUTICAL  ALMANAC  "  OFFICE. 


Narrowness. 


Breadth  of 
view. 


n6 


A  Study  of  the  Sky. 


Not  a  recluse. 


The  value  of 
time. 


Second  after 
second. 


The  director  of  a  large  observatory  is  continually 
brought  into  contact  with  men  who  are  prominent  in 
other  lines  of  scientific  work,  and  with  those  who  have 
won  success  in  various  non-scientific  walks  of  life.  He 
also  looks  after  the  business  interests  of  the  observatory, 
and  sometimes  raises  funds  for  the  enlargement  of  its 
work.  These  circumstances  effectually  prevent  his 
becoming  a  recluse. 

Astronomers  have  an  inordinate  sense  of  the  value  of 
time.  A  business  man  considers  his  own  time  very 
precious  during  business  hours,  and  has  no  welcome 
for  any  one  who  consumes  it  needlessly.  But  after 

business  hours  are 
over  he  is  at  leisure, 
and  whiles  away 
much  of  his  time  in 
pleasurable  o  c  c  u  - 
pations  and  social 
duties.  All  of  an 
astronomer's  wak- 
ing hours,  except 
when  he  is  at  meals, 
are  business  hours. 
So  great  is  the  vol- 
ume of  work  which 
he  would  like  to  do, 
and  so  time-con- 
suming are  the 
laborious  computa- 
tions consequent  upon  his  observations,  that  he  is  con- 
tinually urged  to  work  at  his  topmost  speed.  Every 
minute  counts.  The  very  clocks,  chopping  off  second 
after  second,  within  his  hearing,  remind  him  that  time 
flies,  and  that  his  mind  must  follow  suit.  By  constant 


FIG.  52. — BENJAMIN  A.  GOULD,  EDITOR  OF  THE 
"ASTRONOMICAL  JOURNAL." 


The  Astronomer. 


117 


practice  in  estimating  small  fractions  of  a  second  he 
gains  a  mental  alertness  which  is  carried  into  all  his 
work.  If  he  is  explaining  something,  he  expects  the 
listener  to  grasp  what  he  says  instantly,  and  is  well 
pleased  if  by  any  chance  the  hearer  anticipates  his  ex- 
planation, and  ar- 
rives quickly  at  the 
desired  goal. 

The  following  in- 
cident will  show  how 
this  mental  quicken- 
ing came  to  a  col- 
lege boy.  He  was 
a  member  of  the 
junior  class,  and  be- 
gan a  special  course 
in  practical  astron- 
omy by  learning  to 
take  time  obser- 
vations. This  work 
consists  in  observ- 
ing the  times  that  some  clock  or  chronometer  reads, 
when  certain  known  stars,  in  passing  through  the  field 
of  view  of  a  particular  telescope,  appear  to  cross  a  num- 
ber of  spider-webs  placed  at  the  focus  of  the  glass.  The 
construction  of  the  instrument  will  be  explained  later. 

When  a  star's  image  crosses  each  spider-web,  the 
observer  is  expected  to  note  the  reading  of  his  time- 
piece. When  observing  by  the  ' '  eye-and-ear ' '  method 
he  listens  to  the  ticks  of  the  clock,  and  tries  to  write 
down,  to  the  nearest  tenth  of  a  second,  the  time 
indicated  by  the  clock  when  the  star  crosses  each  web. 
Quickness  of  perception  and  rapidity  of  thinking  are  re- 
quired for  this.  After  the  observations  have  been  made, 


Alertness. 


FIG.  53. — EDWARD  C.  PICKERING,  DIRECTOR  OF 
THE  HARVARD  COLLEGE  OBSERVATORY. 


Sharp  work. 


u8  A  Study  of  the  Sky. 

certain  easy  computations  enable  him  to  find  the  error  of 
the  clock  ;  then  he  compares  this  clock  with  the  other 
timepieces  of  the  observatory,  to  determine  their  errors. 

What  was  the  effect  of  this  work  on  the  college  boy  ? 
He  had  been  an  easy-going  young  man,  who  was 
A  lazy  youth.  content  with  learning  his  lessons  fairly,  and  spending 
the  remainder  of  his  time  in  recreation.  When  on  the 
street  he  had  been  in  the  habit  of  sauntering  along  as 
became  a  gentleman  of  leisure.  When  set  to  do  some 
bit  of  manual  labor  he  had  been  apt  to  distinguish  him- 
self by  the  length  of  time  which  he  consumed  in  the 
task.  He  played  with  his  studies,  as  does  a  cat  with  a 
mouse,  taking  all  the  time  he  wished,  and  being  satisfied 
if  he  was  near  the  head  of  the  class. 

But  now  a  change  came  over  him.  He  set  for  him- 
self a  limited  period  of  time  in  which  each  lesson  must 
A  change.  ke  mastered,  if  possible  ;  he  placed  his  Greek  or  Latin 

text-book  and  his  lexicon  on  the  study-desk  in  such 
positions  that  their  leaves  could  be  turned  quickly.  He 
ceased  his  careless  sauntering,  and  began  to  walk  more 
rapidly.  He  filled  otherwise  unoccupied  chinks  in  the 
day  by  reading  selections  from  the  best  authors.  He 
began  to  speak  with  greater  rapidity  ;  when  reading 
aloud,  it  was  a  mental  strain  for  any  one  to  follow  him, 
for  though  the  words  were  pronounced  clearly,  they 
were  delivered  like  bullets  from  a  machine  gun  ;  he 
could  read  475  words  a  minute.  He  seemed  to  have 
become  thoroughly  imbued  with  a  conviction  that  no 
moments  should  be  wasted,  and  that  as  much  work  as 
possible  must  be  crowded  into  each  minute  of  the  day. 

If  this  was  the  effect  of  a  few  months  of  astronomical 
training  on  a  college  boy,  what  wonder  is  it  that 
astronomers,  after  years  of  such,  work,  gain  special 
mental  quickness  ? 


The  Astronomer. 


119 


Another  characteristic  without  which  no  man  can 
become  an  accomplished  astronomer  is  perseverance. 
At  times  he  plunges  for  weeks  and  months  through 
mazes  of  figures,  the  sight  of  which  fairly  wearies  the 
beholder.  Then  again  he  devotes  himself  to  the  study 
of  some  abstruse  problem  with  such  furiousness  of  appli- 
cation that  he  seems  able  for  the  time  to  think  of 
scarcely  anything 
else.  Fits  of  pro- 
longed abstraction 
seize  him,  and  cu- 
rious are  the  stories 
told  of  his  actions 
when  lost  in  con- 
templation. 

It  is  related  of  Sir 
Isaac  Newton  that 
he  was  once  at- 
tracted by  a  fair 
lady,  and  paid  court 
to  her;  in  the  course 
of  an  evening's  visit 
he  fell  to  musing. 
Reaching  out  his 
hand  he  took  the 
young  lady's  and 
raised  it  gently 
toward  his  lips  ;  he 
carefully  picked  out  the  little  finger  on  which  to  bestow 
the  evidence  of  his  affection.  About  this  time  the  lady 
also  became  lost  in  pleasant  thoughts.  Sir  Isaac 
squeezed  her  finger  a  bit,  and  stirred  the  hot  ashes  of 
his  pipe  with  it.  The  rest  of  the  story  is  short  ;  he  re- 
mained a  bachelor. 


Perseverance. 


FIG.  54.— WILLIAM  H.  PICKERING,  OF  THE 
HARVARD  COLLEGE  OBSERVATORY. 


120 


A  Study  of  the  Sky. 


Accuracy. 


Love  of  truth. 


w«  \ 


Along  with  persistence  goes  a  habit  of  unerring 
accuracy.  The  secret  of  this  is  chiefly  that  the  whole  of 
an  astronomer's  work  tends  to  make  him  concentrate 
his  attention  on  whatever  is  in  hand.  His  whole  mind 
is  usually  occupied  with  the  particular  work  at  which  he 

has  set  himself.  If 
he  is  in  the  midst  of 
the  computation  of 
a  preliminary  orbit 
of  a  comet,  a  single 
incorrect  figure  may 
vitiate  all  the  suc- 
ceeding work  and 
render  his  final  re- 
sults worthless.  So 
well  lubricated  is  his 
mental  machinery 
that  he  goes 
through  intricate 
calculations  without 
becoming  confused, 
or  falling  a  prey  to 
a  haunting  fear  that 
some  blunder  has 
been  committed.  As  there  are  certain  methods  of 
testing  the  answers  of  examples  in  arithmetic,  so  there 
are  occasional  check-formulae,  which  the  computer  may 
use  to  test  his  work  from  time  to  time.  The  application 
of  one  of  these  formulae  rarely  convicts  him  of  error. 

A  habit  of  accuracy  leads  to  love  of  accuracy,  and 
love  of  accuracy  leads  to  love  of  truth  and  hatred  of 
error.  One  cannot  converse  long  with  an  astronomer 
without  noticing  his  love  of  accuracy  and  his  evident 
endeavor  to  tell  the  exact  truth.  He  despises  untruth, 


FIG.  55. — EDWARD  E.  BARNARD,  OF  THE 
YERKES  OBSERVATORY. 


The  Astronomer. 


121 


All  sides  of  a 
question. 


and  is  a  foe  to  prejudice  of  all  kinds.     If  he  hears  a  man 
putting    forth    argument  after  argument   to  bolster   up 
some  position,  his  mind  naturally  begins  to  search  for 
facts  which  are  opposed  to  the  speaker' s  views.     He  has 
an  inward  contempt  for  any  man  who,  instead  of  search- 
ing  for   truth,    occupies   himself  with    elaborating   and 
defending  some   preconceived   notion.      He  applies  all 
reasonable  tests   to  his  own  work,   and   attacks  every 
important  problem  in  as  many  ways  as  feasible,  that  he 
may  obtain  a  series  of  independent  results,  from  which 
the  truth  may  best  be  wrought  out.    When  he  is  engaged 
in    original    investi- 
gation,    intellectual 
honesty  is  his  king. 
Let  us  take  a  con- 
crete illustration   of 
this. 

A  student  who  has 
not  gotten  used  to 
astronomical  ways  is 
measuring  a  certain 
angle.  Each  day  he 
takes  a  set  of  ob- 
servations. His  first 
three  sets  yield  the 
following  values  : 

41°     51'     27".! 

41       51       27  .9 

41        51      27  .o 
He    measures    the 
angle  again  and  ob- 
tains 41°  51'  25". 5.     As  this  does  not  agree  well  with 
the  previous  results  he  feels  disposed  to  reject  it,  and  to  iuandary- 
tell  no  one  about  it,  because  it  apparently  proclaims  him 


FIG.  56. — JAMES  E.  KEELER,  DIRECTOR  OF  THE 
ALLEGHENY  OBSERVATORY. 


A  young  man' 


122 


A  Study  of  the  Sky, 


Rejection  of 
observations. 


Freedom  from 
bias. 


Independence. 


to  be  a  poor  observer.  After  thinking  the  matter  over 
he  asks  the  director  of  the  observatory  what  he  shall  do 
with  the  discordant  measure.  The  director  inquires 
whether  the  observations  seemed  to  be  satisfactory  at 
the  time  when  he  was  making  them,  before  he  knew  the 
result.  The  young  man  replies  that  while  observing  he 
thought  he  was  doing  accurate  work,  and  that  he  does 
not  believe  that  the  instrument  got  out  of  adjustment 
during  the  observations.  The  astronomer  informs  him 
that  if  he  has  no  reason  for  rejecting  the  last  result,  ex- 
cept that  it  does  not  agree  with  the  former  results  as 
well  as  he  would  like  to  have  it,  he  has  no  right  to 
cast  it  out.  Better  to  suffer  the  imputation  of  being  an 
inaccurate  observer  than  to  sacrifice  any  honest  work. 
The  agreement  of  two  or  three  observations  does  not 
prove  that  they  are  nearer  the  truth  than  some  other 
observation,  which  disagrees  with  them. 

If  any  astronomer  were  known  to  be  in  the  habit  of 
giving  a  fictitious  appearance  of  accuracy  to  his  work 
by  suppressing  those  observations  which  exhibited 
noticeable  deviations  from  the  others,  all  his  work  would 
at  once  be  discredited  by  his  scientific  brethren,  who 
would  accuse  him  of  ' '  cooking ' '  his  observations. 
When  one  wishes  to  arrive  at  the  truth  he  must  take 
into  consideration  all  the  evidence,  and  not  reject  some 
of  it,  simply  because  it  does  not  please  him. 

If  scientific  men  did  nothing  for  their  fellows  except 
to  impress  upon  them  the  necessity  of  bringing  un- 
biased minds  to  the  consideration  of  all  important 
questions,  and  of  being  intellectually  honest  in  their 
treatment  of  them,  seeking  the  truth  alone,  their  work 
would  not  be  in  vain. 

There  is  one  more  point  in  this  matter  of  truth 
seeking,  to  which  an  astronomer  pays  special  attention. 


The  Astronomer. 


123 


FIG.  57. — FIRST  POSITION  OF  THE 
SPIDER-WEBS. 


He  strives  to  make  measures  of  the  same  quantity 
independent  of  each  other.  Suppose,  for  example,  that  A  double  star, 
he  is  measuring  a  double 
star.  He  sees  the  two 
stars,  and  two  parallel 
spider-webs.  The  spider- 
webs  are  fastened  in  a 
brass  box,  which  can  be 
turned.  He  wishes  to 
make  the  spider-webs 
parallel  to  a  line  joining 
the  stars.  He  sets  the 
spider-webs  as  in  Fig.  57, 
so  that  it  is  plain  that  they 
are  not  in  the  desired 

position.  He  then  turns  the  brass  box  in  a  left- 
handed  direction,  until  the  desired  parallelism  has 
been  attained,  as  in  Fig.  58.  A  certain  silver  circle, 
which  is  carefully  divided  into  degrees  and  fractions  of  a 

degree,  the  readings  of 
which  change  as  the  box 
holding  the  spider-webs  is 
turned,  is  next  read.  In 
Fig.  59  is  given  a  view  of 
the  rotating  box  and  the 
graduated  silver  circle. 
The  box  is  then  moved 

Anotncr 

again  till  the  spider-webs  measure, 
stand   in   the   position 
shown  in  Fig.  60.     From 
that  position  the  astrono- 
mer brings  them  back  to 

parallelism  with  an  imaginary  line  joining  the  stars,  as 
before,  and  reads  the  circle  again.  By  observing  thus  in 


FIG.  58.— SECOND  POSITION  OF  THE 
SPIDER-WEBS. 


124 


A  Stzidy  of  the  Sky. 


Elimination  of 
bias. 


two  different  ways  he  obtains  more  independent  results 
than  if  he  had  moved  the  spider-webs  in  the  same  di- 
rection each  time.  By  turning  the  box  in  two  opposite 


Self-reliance. 


FIG.  59.— A  MICROMETER. 

directions,  as  he  has  just  done,  he  also  tends  to  elimi- 
nate a  certain  amount  of  personal  bias,  which  would  not 
be  eliminated  if  he  always  turned  the  box  in  the  same 

direction.  He  does  not 
take  many  measures  of 
the  same  double  star  on  a 
given  night,  but  prefers 
to  take  a  few  on  each  of 
several  nights,  thinking 
that  he  will  thus  secure 
greater  independence, 
and  consequently  a  higher 
degree  of  accuracy  in  the 
final  result. 

Practical  astronomical 
work  develops  self-reli- 
ance. A  college  student,  who  has  been  accustomed 
throughout  his  mathematical  course  to  work  examples 
with  the  expectation  of  obtaining  answers  which  agree 


FIG.  60.— THIRD  POSITION  OF  THE 
SPIDER-WEBS. 


The  Astronomer. 


125 


with  those  given  in  the  text-books,  finds  that  there  are 
no  ready-made  answers  to  the  problems  which  a  course 
in  practical  astronomy  presents  for  solution.  Should 
he  become  an  astronomer,  it  will  only  be  after  he  has 
learned  to  say  to  himself,  ' '  This  result  is  right  because 
I  have  worked  it  out  with  care,  and  know  what  I  am 
about." 

Such  words  suggest  conceit,  but  few  classes  of  men   Conceit 
are  less  conceited  than  original  investigators.     A  sciolist 
may   be  extremely 
purled  up.     A  genu- 
ine   man    of  science, 
whose    investigations 
bring  him  to  the  fron- 
tiers  of  knowledge, 
finds    so    many    un- 
explored lands  lying 
before  him  and  so 
many    apparently 
impassable  mountain 
ranges   in    his   path 
that  he  is  forced  into 
an  habitual  attitude 
of  humility.       There 
come  to  mind  the  oft- 
quoted   words   of   Sir    Isaac    Newton  :     "I    know    not 
what  the  world  may  think  of  my  labors,  but  to  myself  it 
seems  that  I  have  been  but  as  a  child  playing  on  the  sea- 
shore ;  now  finding  some  pebble  rather  more  polished, 
and  now  some  shell  rather  more  agreeably  variegated 
than  another,  while  the  immense  ocean  of  truth  extended 
itself  unexplored  before  me. ' ' 

Finally,  what  shall  we  say  about  the  personal  habits   personal 
of  astronomers  ?     Is  an  astronomer  a  good  neighbor  ? 


FIG.  61. — SETH  C.  CHANDLER,  OF  CAM- 
BRIDGE, MASS. 


habits. 


126 


A  Study  of  the  Sky. 


Temper. 


A  literary 
ebullition. 


Usually  he  is  ;  in  rare  instances  he  is  not.  To  be  sure, 
he  often  comes  home  pretty  late,  but  he  has  no  difficulty 
in  fitting  his  latch-key  into  the  proper  place  ;  he  has  not 
been  at  a  carousal.  Sobriety  is  his  habit.  Bleared 
eyes  and  unsteady  hands  are  not  fit  for  astronomical 
work.* 

He  is  usually  quiet,  and  not  easily  roused.  In  the 
comparative  seclusion  of  his  observatory  he  gains  a 
habit  of  calmness.  To  arouse  whatever  is  evil  in  his 
nature  you  have  but  to  interrupt  him  while  he  is  intent 
upon  some  observation.  On  such  an  occasion  he  is 
likely  to  be  short-tempered  and  sharp  of  speech.  He 

reasons  thus :  "A 
business  man  would 
treat  me  with  scant 
courtesy  if  I  asked 
him  to  give  up  his 
business  hours  for 
my  pleasure.  Why 
should  he  not  realize 
that  I  have  business 
hours  as  well  as  he  ?  " 
On  occasions  when 
he  feels  compelled  to 
yield,  he  sometimes 
does  curious  things. 
In  one  of  the  observ- 
ing  books  in  the 
archives  of  an  American  observatory  is  found  this 
sentence,  written  at  such  a  time  :  ' '  Visitors  who  come 
on  working  nights  and  interrupt  a  series  of  observations 


FIG.  62.— SHERBURNE  W.  BURNHAM,  OF  THE 
YERKES  OBSERVATORY. 


*It  is  related  of  an  assistant  in  an  English  observatory  that  once,  when  on  a 
visit  to  this  country,  he  was  found  lying  in  a  gutter,  in  a  state  of  intoxication. 
A  policeman  shook  him  rudely,  and  asked,  "What  are  you  doing  here?" 
''  Observing,  sir,"  was  the  sententious  reply. 


The  Astronomer.  127 


are  undoubtedly  parietosplanchnic  Lamellibranchiates, 
afflicted  severely  with  psittaceous  psychopannychism." 
Such  nonsense  must  have  been  an  effectual  safety-valve 
for  the  writer's  feelings.  On  a  similar  occasion  another 
astronomer  rushed  from  the  dome-room  into  an  adjoin-  An  attack, 
ing  apartment,  seized  a  poker,  and  paced  furiously  up 
and  down  past  the  base-burning  stove  ;  a  fresh  hole 
gaped  in  the  isinglass  whenever  he  went  by. 

Ordinarily,  however,  the  director  of  an  observatory 
treats  visitors  who  come  at  proper  times  with  the  utmost 
courtesy,  and  is  best  pleased  if  they  rain  upon  him  a 
shower  of  questions  about  his  instruments  or  the  celestial 
objects  in  view. 


CHAPTER  VIII. 


Roger  Bacon. 


Hans 
Lippershey. 

Galileo. 


Failures. 


A    GREAT    TELESCOPE. 

"  Through  thee  will  Holy  Science,  putting  off 
Earth's  dusty  sandals  from  her  radiant  feet, 
Survey  God's  beauteous  firmament  unrolled 
Like  to  a  book  new-writ  in  golden  words, 
And  turn  the  azure  scroll  with  reverent  hand, 
And  read  to  man  the  wonders  God  hath  wrought." 

— A.  V.  G. 

THE  great  telescope  of  to-day  has  been  evolved 
during  the  past  three  centuries  by  a  slow  process  of 
growth.  Before  its  actual  invention  many  men  had 
ideas  about  the  possibility  of  making  an  instrument 
which  would  make  distant  objects  appear  near  at  hand. 
Roger  Bacon,  who  died  in  1 294,  stated  that  transparent 
bodies  could  be  made  in  such  forms  and  placed  in  such 
combinations  as  to  magnify  objects.  But  he  never  con- 
structed a  telescope,  for  he  ascribed  to  such  an  instru- 
ment some  properties  which  it  does  not  possess. 

In  1608  Hans  Lippershey,  a  resident  of  Middleburg, 
Holland,  invented  the  telescope.  During  the  ensuing 
year  Galileo  heard  of  the  new  invention,  and  reinvented 
the  instrument.  He  made  several  small  telescopes,  the 
most  powerful  of  which  magnified  thirty-three  diameters, 
and  revealed  the  spots  on  the  sun,  the  lunar  mountains, 
the  moons  of  Jupiter,  and  the  phases  of  Venus. 

Slight  progress  was  made  during  the  next  hundred 
years.  Men  failed  to  get  clear,  sharp  images  of  objects, 
no  matter  how  accurately  they  ground  the  lenses  of 

128 


A   Great   Telescope. 


129 


their  telescopes.     Even  the  immortal  Newton  was  foiled.    Newton  foiled. 
When   he  discovered    that   white    light   was   dispersed 


FIG.  63.— THE  YERKES  TELESCOPE  AT  THE  COLUMBIAN  EXPOSITION. 

into   a   number   of    different   colors    by    being   passed   Dispersion  of 
through  a  prism,  he  also  found  that  passage  through  a  llght> 


130 


A  Study  of  the  Sky. 


Newton's 
reflector. 


Lord  Rosse's 
reflector. 


Silver  on  glass.    . 


lens  affected  it  in  the  same  way.  Believing  that  the 
dispersed  rays  could  not  be  reunited,  Newton  gave  up 
all  hope  of  perfecting  Galileo's  form  of  telescope,  and 
turned  his  attention  to  making  concave  mirrors,  which 
reflected  the  light  to  a  focus  without  dispersing  it. 
Newton's  first  reflecting  telescope  was  six  inches  long, 
and  was  equipped  with  a  mirror  one  inch  in  diameter. 
So  successful  was  the  performance  of  this  pigmy  that  he 
made  a  larger  one,  which  is  now  in  the  possession  of 

the  Royal  Society  of 
London,  and  bears 
this  inscription: 
"The  first  reflecting- 
telescope,  invented 
by  Sir  Isaac  Newton, 
and  made  with  his 
own  hands." 

As  the  years  rolled 
on,  reflecting  tele- 
scopes of  larger  and 
larger  sizes  were 
made,  until  at  last 
Lord  Rosse's  levia- 
than, which  has  a 
mirror  six  feet  in  di- 
ameter, was  mounted  at  Parsonstown,  Ireland,  fifty  years 
ago.  No  other  reflector  of  equal  size  has  yet  been  con- 
structed. Its  mirror  was  made  of  polished  metal.  It  is 
now  customary  to  make  the  mirror  of  glass,  and  to  coat 
it  with  silver. 

Such  telescopes  offer  special  advantages  for  photo- 
graphic and  spectroscopic  work,  since  the  light  which 
impinges  upon  a  mirror  suffers  no  dispersion,  as  it 
would  if  passed  through  a  lens. 


FIG.  64.— ALVAN  G.  CLARK,  OPTICIAN,  OF 
CAMBRIDGE,  MASS. 


A   Great  Telescope.  131 

Since  reflectors   are   little   used   in  this  country,   we 
return  to  the  history  of  the  common  form  of  telescope,    A  refractor, 
which  is  called  a  refractor.     The  name  refractor  arises 
from  the  fact  that  rays  of  light,   in  passing  through  a 
lens,  are  bent,  or  "  refracted. " 

We  have  noticed  that  Newton  thought  it  impossible 
to  reunite  the  rays  of  various  colors  which  were  scat- 
tered in  passing  through  his  lenses.  But  early  in  the 
eighteenth  century  a  well-to-do  countryman  of  his,  Mr. 
Chester  Moor  Hall,  was  struck  with  the  fact  that  the 
human  eye,  which  contains  more  than  one  refractive 
medium,  produces  images  practically  free  from  obnox- 
ious color  fringes.  By  combining  two  lenses  of  different 
kinds  of  glass  he  reunited  the  dispersed  rays  pretty  well. 
Being  a  gentleman  of  leisure,  he  took  no  particular  pains 
to  follow  up  his  discovery,  and  the  credit  of  it  was  soon 
given  to  Mr.  John  Dollond,  an  optician,  who  experi- 
mented successfully  along  similar  lines  and  published  an 
account  of  his  work  in  1758. 

A  new  difficulty  of  the  first  magnitude  now  arose.    A  new  diffi. 
Good  discs  of  glass  more  than  three  and  a  half  inches  in   culty> 
diameter  could  not  be  procured.     In  vain  the  French 
Academy    offered    prizes    for    larger   discs  ;    the   best 
chemists  were  baffled.     But  the  battle  is  not  always  to 
the  strong.     From  1784  to  1814,  Guinand,  a  poor  Swiss 
watchmaker,  toiled  with  dauntless  industry,  overcoming 
one  obstacle  after  another,  until  he  succeeded  in  produ- 
cing glasses  eighteen  inches  in  diameter. 

The  manufacture  of  a  large  disc  of  optical  glass* 
requires  the  utmost  carefulness,  as  well  as  a  high  degree 

*  There  are  now  only  three  firms  in  the  world  which  have  made  very  large 
lenses,  Chance  &  Co.,  of  Birmingham,  Mantois  of  Paris,  and  Schott  &  Co.,  of 
Jena.  Schott  &  Co.  now  produce  a  number  of  different  kinds  of  glass,  and  a 
large  amount  of  experimentation  is  going  on,  in  an  endeavor  to  find  combina- 
tions of  lenses  which  will  give  more  satisfactory  results  than  the  time-honored 
•combination  of  a  lens  of  crown  glass  backed  up  by  another  one  of  flint  glass. 
Professor  Hastings,  of  Yale,  has  been  successful  in  such  researches. 


132 


A  Study  of  the  Sky. 


The  materials 
melted. 


The  stirring. 


The  furnace 
luted. 


of  technical  skill.  Nineteen  trials  were  made  for  one  of 
the  lenses  of  the  36-inch  Lick  object-glass,  before  suc- 
cess was  attained. 

A  pot  made  of  very  pure  clay  is  heated  to  a  high 
temperature,  and  gradually  filled  with  a  batch  of  the 
raw  materials.  After  the  batch  seems  to  be  thoroughly 
melted  a  portion  of  it  is  taken  out  and  examined,  to  see 
if  any  unmelted  particles  of  silica  remain,  or  if  there  are 
minute  air-bubbles,  which  have  not  been  expelled  by 
the  heat. 

Should  neither  of   these  defects  be  discovered,   the 

melted  glass  is 
stirred  with  an  iron 
rod,  the  lower 
portion  of  which  is 
covered  with  clay. 
The  stirring  is  con- 
tinued for  two  or 
three  hours,  until 
the  cooling  glass 
resists  further  ma- 
nipulation. The 

FIG.  65.-LuMP  OF  OPTJCAL  GLASS.  twQ  workmen,  who 

swelter  in  the  furnace  heat  while  executing  this  opera- 
tion, must  not  allow  the  stirrer  to  touch  the  pot ;  for 
bits  of  clay  might  be  ground  off  and  mixed  with  the 
glass. 

The  glass  is  reheated,  stirred  a  second  time  and  even 
a  third  time,  and  returned  to  the  furnace.  Every  open 
place  in  the  furnace  is  stopped  up,  so  that  no  air  may 
gain  admittance,  and  the  whole  is  allowed  to  cool  for 
several  days,  that  it  may  not  crack.  A  rapid  cooling 
would  cause  it  to  be  shattered  into  small  fragments. 

When  the  cooling  is  finished  the  glass  is  examined, 


A   Great  Telescope. 


133 


FIG.  66.— THE  LUMP  CUT  DOWN. 


and   any  defects  which  may   be  apparent  are  ground 

away,  or  sawed  off.     An  imperfect  spot  near  the  center   J.'utPoSections 

of  the  disc  may  be  sawed  out,  if  the  chunk  of  glass  is 

not    sawed    clear 

through. 

The  accompany- 
ing   figures    show 
the  block  of  glass 
from   which  the 
crown  disc  of  the 
forty-inch    Yerkes 
telescope  was  ob- 
tained.    Fig.  65  is 
the  original  lump. 
Fig.    66   shows   it 
after  some  imperfections   have  been   sawed  off.       The 
lump  is  now  to  be  molded  into  the  shape  shown  in  Fig.    A  forty-inch 
67.     The  glass  is  put  into  a  mold,  which  is  placed  in  a  d 
special  furnace  and  heated  very   slowly.       At  last  the 

glass  softens  and 
adapts  itself  to  the 
shape  of  the  mold. 
The  temperature  is 
lowered  to  about 
i,  200°  Fahrenheit, 
and  every  opening 
in  the  furnace 
stopped  up  ;  after 
an  exceedingly 
slow  and  careful 
FIG.  67.-THE  LUMP  MOLDED.  c  o  o  1  i  n  g  the  ten- 

sided  block  is  removed  and  examined.  Fresh  imper- 
fections are  discovered  and  cut  away,  as  Figs.  68  and 
69  testify.  The  defects  may  be  of  such  a  nature  that 


134 


A  Study  of  the  Sky. 


the  disc  must  be  reheated  and  molded  again,  but  if  too 
many  annealings  are  attempted,  the  glass  may  lose  its 
transparency.  After  months  of  labor  the  original  shape- 

less  mass  is  re- 
duced to  a  beauti- 
ful circular  disc. 

A  few  small  bub- 
bles, or  bits  of  grit, 
while  they  mar  the 
appearance  of  a 
disc,  have  no  per- 
ceptible deleter- 
ious, effect 


Bubbles. 


in    a 
finished  lens.  They 

FIG.  68.—  THE  LUMP  AFTER  FURTHER  CUTTING,     prevent     the     pas- 

sage  of  a  certain  minute  quantity  of  light,  and  theo- 
retically injure  the  perfection  of  the  image  of  an  object 
seen  through  the  lens. 

striae.  When  a  careful  test  is  made  '  *  striae,  '  '  or  veins,  may  be 

found    in    the    in-   |B| 
terior  of  the  lens  ;   || 
should  these   be 
numerous  or  pro- 
nounced  the   lens 
must   be  rejected. 
The   glass   may. 
have      passed 
through  all   these 
tests   and   yet    be 
worthless.     If  the 

process  of   COOlinP" 

was  not  conducted  with  sufficient  care  the  glass  may 

internal  strain,    have  solidified  in  a  state  of  dangerous  internal  strain. 

To  test  for  this  the  glass  is  laid  upon  a  piece  of  dark 


^PIG>  ^9-  —  THE  LUMP  CUT  DOWN  STILL  MORE. 


A   Great  Telescope. 


135 


cloth,  in  some  place  where  there  is  suitable  light,  and 
examined  by  a  Nicol's  prism.  If  a  pronounced  dark 
cross  is  seen  in  the  glass,  the  internal  strain  is  too  great, 
and  the  glass  must  not  be  used  for  a  telescope. 

The  glass-founder   has  now  finished   his  part  of  the  The  optician's 

work. 

work,  and  the 
disc,  if  sufficiently 
perfect,  is  turned 
over  to  the  op- 
tician, who  is  to 
fashion  its  curves 
so  accurately  that 
the  rays  of  light 
from  a  distant 
star  may  be  con- 
verged by  it  to  a 
point  which  can 
be  covered  with 
a  spider's  web. 

The  rough  grinding  is  done  with  a  cast-iron  tool,  The  grinding, 
similar  in  appearance  to  the  one  lying  on  the  floor  in  the 
illustration  (Fig.  70).  If  a  convex  surface  is  to  be  pro- 
duced on  the  glass,  the  tool  is  hollowed  out  and  made 
of  the  proper  degree  of  curvature.  The  usual  grinding 
material  is  emory,  which  is  placed  between  the  tool  and 
the  glass.  A  better  material  is  obtained  by  driving  a 
blast  of  air  into  melted  iron.  A  cloud  of  minute 
particles  of  iron  is  blown  out ;  being  chilled  by  contact 
with  the  air  they  settle  down  as  a  very  fine  powder. 

After  the  lens  has  been  brought  nearly  to  the  proper  The  polishing< 
shape  it  is  placed   upon   the   machine   shown  in  Fig. 
70   to   be   brought   to    its   proper   form   by   polishing. 
The  tool,  which  lies  upon  the  lens,   is  similar  to  the 
former  one,  except  that  its  face  is  composed  of  squares 


FIG.  70.— MACHINE  FOR  POLISHING  LENSES. 


1 36 


A  Study  of  the  Sky. 


The  testing. 


An  artificial 
star. 


of  pitch,  instead  of  squares  of  cast-iron.  The  lens  lies 
on  a  table  which  turns  slowly.  The  tool  is  moved  by 
two  wooden  rods,  each  of  which  is  driven  by  a  crank  at 
its  further  extremity ;  the  cranks  are  of  different  lengths, 
and  turn  at  widely  different  rates.  So  complicated  is 
the  motion  that  the  tool  never  describes  the  same  path 
twice.  When  the  surface  has  been  brought  to  a  brilliant 
polish,  the  lens  appears  to  be  finished. 

But  the  most  difficult  part  of  the  process  is  yet  to 
come.     The  surface,  which  looks  perfectly  spherical,  is 


FIG.  71.— ALVAN  CLARK'S  WORKSHOP. 

probably  too  high  in  certain  regions  and  too  low  in 
others  ;  these  inequalities  must  receive  attention.  A 
spherometer  which  will  measure  TBVTSTI  of  an  inch  is  too 
rude  to  measure  them.  The  lens  is  set  up  on  edge  in  a 
special  testing  room,  where  the  temperature  is  not 
subject  to  sudden  variations  ;  light  from  a  lamp  shining 
through  a  small  hole  is  sent  through  the  lens,  and 
impinges  on  a  mirror,  which  reflects  it  back  again 
through  the  glass  to  the  eye  of  the  optician.  To  him 
the  entire  lens  appears  to  be  aflame  with  light.  If  it  is 


A   Great   Telescope. 


137 


not  uniformly  bright  all  over,  its  shape  is  not  perfect. 
Imperfect  portions  cause  dark  spots  in  the  midst  of  the 
general  brightness.      Perhaps  some  part  of  the  surface  is 
too  high  and  must  be  polished  down  ;  perchance  it  is 
too  low,  and  the  rest  of  the  surface  must  be  brought 
down  to  it.     From  the  testing  room  to  the  polisher  and 
back  again  the  lens 
must  go,  till  the  op- 
tician is  satisfied 
with  its  perform- 
ance.    At  times  the 
operator  rubs  down 
some   protuberant 
portion  with  his 
hand. 

If  the  lens  is 
touched  with  one 
fi  n  g  e  r  for  a  few 
seconds,  during  the 
process  of  testing, 
the  heat  thus  com- 
municated to  the 
lens  raises  an  intol- 
erable lump  in  it, 
which-  will  not  dis- 
appear till  that  por- 
tion of  the  glass  has 
cooled  again.  A  zone  which  is  elevated  three  or  four 
millionths  of  an  inch  must  not  be  neglected. 

The  final  shaping  of  the  lens  ordinarily  involves  the  Final  touches, 
expenditure  of  so  much  time  that  the  cost  of  rubbing  off 
a  given  quantity  of  the  material  is  one  thousand  times  as 
great  as  the  cost  of  taking  off  an  equal  quantity  by  the 
first  process  of  rough  grinding. 


FIG.  72. — JOHN  A.  BRASHEAR,  OPTICIAN,  OF 
ALLEGHENY,  PA. 


138 


A  Study  of  the  Sky. 


The  finished  object-glass  is  put  into  a  cast-iron  cell  ; 
Placed  in  a  cell,  the  edges  of  the  two  lenses  composing  the  object-glass 
do  not  touch  the  cast-iron  ;  each  of  them  rests  against  a 
silver  surface  on  the  inside  of  the  cell  ;  otherwise  a  little 
corrosion  of  the  iron  might  damage  the  glass.  The  cell 
is  then  ready  to  be  fastened  to  the  steel  tube  of  the 
telescope. 

The  instrument  maker  has  an  important  work  to  per- 
form before  the  great  lens  can  be  set 

"  Like  a  star  upon  earth's  grave  and  cloud-encircled  brow." 

He  must  make  such  a  mounting  that  the  telescope  can 
be  readily  directed  to  any  point  in  the  sky  ;  further- 
more, the  telescope  must  move  automatically  in  such  a 

way  that  a  star  may  be 

kept 

view 


The  mounting. 


The  earth's 

rotation 

counteracted. 


An  odd  axis. 


Of 


FIG.  73.— THE  Two  LENSES  OF  AN  OBJECT- 


in    the    field 
for  hours. 
Since  the  earth  ro- 
tates, and  carries   the 


GLASS.  telescope  with  it,  the 

latter,  if  directed  toward  a  given  star,  at  any  instant, 
will  point  in  quite  a  different  direction  a  minute  after- 
ward. The  mechanician  must  therefore  counteract  the 
rotation  of  the  earth. 

For  purposes  of  explanation  it  is  best  to  consider  the 
earth  as  fixed  and  the  celestial  sphere  as  rotating  about 
an  axis  drawn  from  the  north  celestial  pole  to  the  south 
celestial  pole.  This  conception  has  already  been  pre- 
sented in  Chapter  II.  Imagine  this  axis  to  be  a  wooden 
shaft  six  inches  in  diameter,  rotating  steadily,  making 
one  turn  in  twenty-four  hours,  and  carrying  the  celestial 
sphere  with  it. 

If  a  lath  be  nailed  to  this  shaft  in  such  a  position  that 
it  points  to  Sirius,  it  will  continue  to  point  toward  Sirius 


A   Great  Telescope. 


139 


day  after  day,  as  the  shaft  and  sphere  rotate  together. 
This  is  the  fundamental  idea  upon  which  the  mechan-  A  9teel  shaft- 
ician  seizes.  He  quickly  perceives  that  he  can  set  up  a 
short  shaft  of  steel, 
which  shall  point  to 
the  north  celestial 
pole,  and  resemble  a 
section  of  the  wooden 
shaft  which  we  have 
been  considering.  By 
s  u  i  table  mechanism 
he  can  rotate  the  steel 
shaft  once  in  twenty- 
four  hours.  Then  if 
he  can  attach  the  tel- 
escope to  this  shaft 
in  such  a  way  that  it 
can  be  pointed  in  any 
direction,  the  prob- 
lem is  solved. 

The  fundamental 
shaft  which  points 
toward  the  celestial 
poles,  and  is  parallel 
to  the  earth's  axis,  is 
called  the  polar  axis, 
and  is  shown  on  top 
of  the  pillar  in  Fig. 
74  ;  it  is  below  the 
telescope  and  parallel 
to  it.  To  the  upper 
end  of  the  polar  axis  is  fastened  a  long  " sleeve,"  at 
right  angles  to  it.  Inside  this  sleeve  turns  another  axis,  moundng°rial 
called  the  declination  axis,  at  the  lower  end  of  which  a 


FIG.  74.— AN  EQUATORIAL  TELESCOPE. 


140 


A  Study  of  the  Sky. 


Ingenious 
contrivances. 


Accurate 
workmanship. 


Various 
materials. 


lamp  is  shown  in  the  figure.  The  declination  axis  carries 
a  heavy  weight,  to  balance  the  weight  of  the  telescope, 
so  that  the  entire  structure  may  be  nicely  poised  on  the 
polar  axis.  The  telescope  is  fastened  to  the  declination 
axis,  and  is  at  right  angles  to  it.  On  each  axis  there  is 
a  graduated  circle  ;  by  these  the  astronomer  sets  the 
telescope  so  that  it  points  toward  any  object  whose  right 
ascension  and  declination  are  known.  The  clock-work 
for  rotating  the  polar  axis  lies  under  it,  and  is  driven  by 
a  weight  concealed  in  the  hollow  pillar  which  supports 
the  instrument. 

A  large  instrument  of  this  kind  is  very  complicated, 
and  fairly  bristles  with  ingenious  contrivances  to  facili- 
tate the  work  of  the  exacting  individual  who  is  to  use  it. 
When  an  astronomer's  eyes  first  rest  upon  a  great 
telescope,  with  which  it  is  to  be  his  good  fortune  to 
storm  the  sky,  his  sensations  are  of  the  liveliest  charac- 
ter. The  mass  of  steel,  iron,  and  brass  which  confronts 
him  speaks  eloquently  of  the  patient  ingenuity  of  the 
mechanician  who  calculated  the  form  and  dimensions  of 
each  of  the  hundreds  of  pieces  of  metal  which  are  joined 
in  the  intricate  mechanism,  and  subordinated  them  all  to 
one  great  purpose. 

It  also  tells  of  the  painstaking  care  of  many  skilful 
workmen,  who  have  toiled  thousands  of  hours  perfect- 
ing the  teeth  of  the  gears,  polishing  the  pivots  and 
bearings,  making  the  various  screws  true,  and  fitting  all 
together,  to  form  a  harmonious  whole. 

Not  only  must  the  different  parts  be  correctly  pro- 
portioned, but  each  must  be  made  of  the  proper 
material.  Steel  of  various  degrees  of  hardness,  cast- 
iron,  wrought-iron,  brass,  copper,  lead,  phosphor- 
bronze,  silver,  German  silver,  nickel,  hard  rubber, 
wood,  carbon,  glass,  vegetable  fiber,  and  even  spider- 


A   Great  Telescope. 


141 


webs  all  occupy  their  proper  places.     At  some  points 
friction  is  relieved  by  ball-bearings  ;  at  others  by  friction   Friction, 
rollers  ;  at  still  others  friction  must  have  full  play. 


FIG.  75.— THE  CHAMBERLIN  TELESCOPE  OF  THE  UNIVERSITY  OF  DENVER. 

The  tons  of  metal  which  compose  the  moving  parts  of  Electric 
the  great  Yerkes  telescope  are  moved  in  any  direction,  motors- 
swiftly  or  slowly,  by  means  of  electric  motors.  The 


142  A  Study  of  the  Sky. 

astronomer   presses   the   button,    the    motor   fulfils   his 
bidding. 

Fig.  75  shows  a  large  telescope  ready  for  work.  The 
^telescope  in  pillar  goes  through  the  floor  without  touching  it,  and 
rests  on  a  stone  pier  below.  Near  the  bottom  of  the 
pillar  are  two  hand-wheels,  by  means  of  which  the  tele- 
scope can  be  moved  quickly  into  any  desired  position. 
Above  them  is  a  box  containing  clock-work  which 
indicates  the  right  ascension  and  declination  of  any 
object  at  which  the  telescope  is  pointing.  Through  a 
glass  door  in  the  uppermost  section  of  the  pillar  one 
may  see  the  driving  clock.  The  declination  axis  is 
behind  the  tube.  The  observing  platform,  which  slides 
up  and  down  along  an  inclined  runway,  is  shown  at  the 
left.  The  overarching  iron  dome  rests  upon  anti- 
friction wheels,  which  are  on  top  of  the  stone  wall. 


CHAPTER    IX. 
/  / 

THE  ASTRONOMER'S  WORKSHOP  AND  SOME  OF  HIS 
TOOLS. 

"  Go  to  yon  tower,  where  busy  science  plies 
Her  vast  antennae,  feeling  thro'  the  skies  ; 
That  little  vernier,  on  whose  slender  lines 
The  midnight  taper  trembles  as  it  shines, 
A  silent  index,  tracks  the  planets'  march 
In  all  their  wanderings  thro'  the  ethereal  arch, 
Tells  through  the  mist  where  dazzled  Mercury  burns, 
And  marks  the  spot  where  Uranus  returns." 

— Holmes. 

AN  astronomical  observatory  is  conspicuous  among  An  observatory 
surrounding  structures  by  its  unusual  appearance.  One 
or  more  domes  surmounting  it  catch  the  eye  at  once. 
There  are  long  narrow  doors  in  the  walls  and  shutters 
on  the  roof,  which  arrest  attention.  Fig.  76  is  a  repre- 
sentation of  an  observatory. 

First  as  to  the  site.  The  location  is  usually  not  a 
matter  within  the  astronomer's  control ;  he  is  fortunate 
if  he  is  even  allowed  to  plan  the  building,  so  as  to 
adapt  it  to  the  purposes  to  which  it  is  to  be  devoted.  If 
he  had  his  choice  of  location,  he  would  be  likely  to 
choose  a  considerable  elevation. 

A  mountain  top  would  seem  most  suitable  were  it 
available  ;  but  experience  shows  that  such  is  not  usually  A  mountain, 
the  case.  The  advantage  is  that  the  observer  is  above 
quite  a  thickness  of  atmosphere,  so  that  the  stars  shine 
out  more  clearly,  and  faint  objects  are  more  distinctly 
visible.  But  the  disadvantages  are  many.  On  a  moun- 

143 


i44 


A  Study  of  the  Sky. 


tain  top  the  air  is  almost  always  in  motion  ;  warm 
currents  rush  up  the  sides  of  the  mountain,  and  cooler 
air  descends.  The  expansion  of  the  warm  and  vapor- 
laden  air,  which  comes  from  below,  chills  it,  and  pro- 


FIG.  76.— THE  YERKES  OBSERVATORY. 

duces    mists,    or   even    clouds,    which    hang  about   the 
summit. 

obtrusive  Even  when  no  mist   forms,   whirling  currents  come 

currents  of  air.  between  the  telescope  and  the  celestial  object  toward 
which  it  is  pointed.  The  light  from  the  object,  in  pass- 
ing through  these  changing  currents,  is  bent  hither  and 
thither,  so  that  the  object  appears  to  dance,  and  to 
be  distorted  ;  no  satisfactory  view  of  it  is  possible. 
Furthermore  the  wind  shakes  the  telescope  itself,  and 
renders  accurate  observations  out  of  the  question.  It  is 
generally  admitted  that  an  ideal  site  is  an  elevated 
plateau  ;  the  farther  it  is  from  a  mountain  range  the 
better  ;  a  dry  atmosphere  is  also  considered  advan- 
tageous. 

Where  circumstances  limit  the  location  to  the  neigh- 
borhood of  some  city,  a  study  of  the  prevailing  winds  is 
made,  so  that  the  evil  of  the  city's  smoke  may  be 
minimized.  A  spot  of  ground  embracing  a  few  acres, 
so  that  other  buildings  may  not  be  built  too  near  the 


The  environs  of 
a  city. 


The  Astronomer1  s  Workshop. 


observatory,  and  commanding  a  fair  sweep  of  the 
horizon,  is  sought.  It  is  advisable  to  avoid  proximity 
to  railroads,  because  of  the  earth  tremors  caused  by  the 
passage  of  heavy  trains. 

When  the  site  has  been  chosen  and  the  instrumental 
•equipment  determined  upon,  the  building  is  so  planned 
as  to  furnish  a  suitable  home  for  the  instruments,  and 
working  quarters  for  the  astronomer.  The  building 
shown  in  the  illustration  (Fig.  77)  faces  southward 
because  the  large  telescope  under  the  dome  is  chiefly 
used  for  observing  objects  in  the  south,  east,  or  west, 
and  is  not  often  pointed  northward.  Were  the  building 
turned  around,  the  observer  would  have  to  look  over 
some  portion  of  the  roof  most  of  the  time.  From  the 
roof,  which  has'  been  heated  during  the  day,  arise  cur- 
rents of  warm  air  which  would  disturb  telescopic  vision. 


The  building. 


FIG.  77.— THE  CHAMBERLIN  OBSERVATORY. 

To  avoid  these  as  much  as  possible  the  wings  of  the 
building  are  set  back. 

The    meridian    circle,    the    instrument    next   in    im- 

The  transit 

portance,  is  now  to  be  provided  for.     Shall  it  be  in  the  room- 
east  wing  or  in  the  west  ?     If  it  is  put  in  the  west  wing, 


146 


A  Study  of  the  Sky. 


The  clocks. 


Temperature 
and  humidity. 


Special 
supports. 


which  is  heated  up  by  the  afternoon  sun,  observations 
in  the  early  evening  will  be  vitiated  by  the  currents  of 
warm  air  rising  all  about  it.  The  east  wing,  on  the 
other  hand,  is  largely  protected  from  the  sun  in  the 
afternoon,  being  in  the  shadow  of  the  rest  of  the  build- 
ing. This  instrument  is  therefore  installed  in  the  east 
wing  ;  a  continuous  slit  is  cut  in  the  roof  and  in  the 
north  and  south  walls,  so  that  the  telescope  may  survey 
the  entire  meridian  from  the  north  point  of  the  horizon 
up  to  the  zenith,  and  down  to  the  south  point.  When 
the  instrument  is  not  in  use  the  slit  is  closed  by  doors. 

The  clocks  are  next  to  be  suitably  housed.  Shall 
they  be  put  in  the  west  wing  ?  By  no  means.  For  the 
heat  of  the  afternoon  sun  would  cause  them  to  change 
their  rates.  Fine  clocks  are  supposed  to  be  so  con- 
structed that  changes  in  the  temperature  will  not  cause 
them  either  to  gain  or  to  lose.  But  no  clock  has  yet 
been  made  which  will  not  change  its  rate  under  varia- 
tions of  temperature.  Why,  then,  shall  they  not  be 
placed  in  the  deep  basement  underneath  the  tower, 
below  the  surface  of  the  ground,  where  the  thermometer 
will  probably  not  vary  5°  a  day,  in  ordinary  weather? 
In  that  location  there  will  be  another  foe  to  fight  ;  for  a 
cellar,  even  though  it  be  surrounded  by  a  stone  wall  two 
feet  thick  and  have  a  cement  floor,  is  damp.  The 
delicate  mechanism  of  the  clocks  will  suffer  from  this 
cause.  The  clocks  must  not  stand  on  the  floor  or  be 
hung  upon  wooden  partitions.  Special  piers  must  be 
built  to  support  them,  unless  there  is  some  other 
adequate  provision  for  them. 

In  order  to  avoid  changes  of  temperature  a  portion  of 
the  round  tower  is  partitioned  off,  on  the  main  floor. 
The  space  shown  in  Fig.  78  is  so  selected  that  no  wall 
of  the  clock-room,  except  a  very  short  length,  where 


The  Astronomer1  s  Workshop. 


147 


two  windows   are,  is  an  outside  wall  of   the    building. 

These  two  windows  are  made  double,  and  covered  with   The  dock- 
room. 

wooden  shutters.  Thus  both  the  sun's  rays  and  the 
storms  of  winter  are  guarded  against.  If  the  clocks 
were  hung  on  the  stone  wall  which  partly  bounds  the 
room,  the  turning  of  the  dome,  which  rests  on  this  wall, 


FIG.  78. — MAIN  FLOOR  OF  THE  CHAMBERLIN  OBSERVATORY. 

might  jar  them  a  trifle.  Therefore  the  great  pier  in  the 
•center  of  the  tower  is  utilized.  Stout  beams  are  built 
into  the  pier,  and  project  through  the  thin  partition  into 
the  clock-room  ;  the  beams  do  not  touch  the  partition, 
for  in  that  case  the  vibrations  of  the  floor,  as  people 
walk  about  on  it,  would  shake  the  clocks. 

The  west  wing  contains  the  study  of  the  astronomer.    The  study. 


148 


A  Study  of  the  Sky. 


The  basement. 


Foundations 
and  floors. 


The  upper 
story. 


No  heat. 


He  does  not  care  for  the  heat  of  the  long  summer  after- 
noons, if  the  instruments  are  protected  from  it. 

In  the  basement  arrangements  are  made  for  the  heat- 
ing plant,  which,  if  one  has  plenty  of  money  to  spend,  is- 
a  hot-water  system  ;  also  for  a  photographic  dark-room, 
battery-room,  janitor's  quarters,  storeroom,  and  work- 
shop. A  good  carpenter's  bench  and  a  small  kit  of 
tools  are  needed.  If  the  observatory  is  a  large  one,  a 
lathe  and  other  machines  for  working  metals  are  a  part 
of  the  equipment.  Quite  a  little  of  the  basement  is  oc- 
cupied by  the  piers  on  which  the  instruments  rest. 

The  foundations  of  these  are  sunk  pretty  deep,  the 
depth  depending  upon  the  character  of  the  soil.  A 
gravel  bed  makes  an  excellent  foundation  ;  rock  or  hard 
clay  is  also  satisfactory,  except  that  they  readily  trans- 
mit vibrations  arising  from  the  passage  of  railroad  trains 
within  half  a  mile,  or  heavy  traffic  in  a  neighboring 
street.  The  floors  must  not  touch  any  of  the  piers,  for, 
in  that  case,  the  vibrations  caused  by  human  footfalls 
will  be  communicated  to  the  piers  and  thus  to  the 
instruments.* 

In  the  upper  story  of  the  observatory  the  principal 
room  is  the  dome-room,  the  home  of  the  great  telescope. 
On  a  level  with  the  floor  of  this  room  is  an  extensive  bal- 
cony from  which  one  can  glance  at  all  parts  of  the  sky. 
Two  or  three  small  rooms  adjoin,  where  various  attach- 
ments of  the  telescope  are  kept,  and  where  the  observer 
may  occasionally  warm  himself  on  a  bitter  night. 

It  is  not  practicable  to  heat  the  dome-room,  for  the 


*  Before  the  telescope  of  the  Chamberlin  Observatory  was  installed,  the  floor 
of  the  dome-room  was  shored  up  on  the  great  pier,  so  that  it  might  not  sag 
when  the  various  parts  of  the  telescope  were  laid  on  it,  preparatory  to  being 
put  together.  After  the  telescope  was  mounted,  the  props  were  forgotten  for 
a  time,  and  every  star  under  observation  danced  about  in  a  most  dishearten- 
ing manner,  as  people  walked  about  the  room.  In  a  few  days  the  props  were 
remembered  and  knocked  out.  The  trouble  ceased  at  once.  The  stone  pier 
which  had  been  so  shaken  weighs  320  tons. 


The  Astronomer 's  Workshop.  149 

heated  air  would  escape  through  the  slit,  when  the  dome 
shutter  was  rolled  off.  Nor  is  it  allowable  to  experiment 
in  this  direction,  because  a  current  of  warm  air  rising  in 
front  of  the  large  glass  would  cause  the  stars  to  appear 
blurred  and  to  dance  about  in  such  fashion  that  no  satis- 
factory views  of  them  could  be  had. 

Domes  more  than  thirty-five  feet  in  diameter  are  built  Domes, 
of  iron.  They  are  made  as  light  as  is  consistent  with  a 
proper  degree  of  rigidity,  and  are  covered  with  heavy 
galvanized  iron.  Great  care  is  taken  to  mount  them  in 
such  a  manner  that  they  will  rotate  with  ease.  An 
astronomer  whose  strength  has  been  exhausted  by  turn- 
ing an  unmanageable  dome  is  in  no  physical  condition 
to  manipulate  a  delicate  instrument,  the  smallest  reading 
of  which  corresponds  to  a  distance  of  -STS^SV  of  an  inch. 

Where  a  good  current  of  electricity  and  a  small  elec- 
tric motor  are  available,  the  observer  has  but  to  touch  a  A  rising  floor, 
push  button,  and  the  dome  revolves.  For  very  large 
telescopes,  the  floor  of  the  dome-room  is  made  of  iron, 
and  is  raised  or  lowered  by  powerful  machinery,  which 
may  be  started  and  stopped  by  pressing  a  button. 

Some  of  the  astronomer' s  tools  are  so  important  and  Some  of  the 
so  common  that  we  must  examine  them.     The  great  SJj°nomer>s 
telescope  which  was  described  in    the    last  chapter   is 
much  too  cumbersome  to  be  used  in  the  most  refined  in- 
vestigations  for  determining  the  right  ascensions   and 
declinations  of   ' '  fundamental  stars. ' '     The  instrument 
used  for  this  purpose  is  comparatively  small,  extremely 
rigid,  and  so  mounted  that  it  can  view  a  celestial  object 
only  when  the  latter  is  near  the  meridian. 

Fig.  79  shows  that  the  instrument  consists  of  a  tele- 
scope, which  is  perpendicular  to  a  horizontal  axis.  The 
axis  points  east  and  west  and  terminates  in  two  cylin- 
drical steel  pivots,  each  of  which  rests  in  a  wedge-shaped 


150 


A  Study  of  the  Sky. 


The  graduated 
circles. 


Measurement 
of  angles. 


metal  bearing  called  a  V,*  from  its  resemblance  to  that 
letter.  These  bearings  are  fastened  very  securely  to  two 
substantial  piers,  generally  of  stone. 

Upon  the  axis  are  mounted  two  circles,  one,  at  least, 
of  which  carries  a  band  of  silver,  on  which  fine  marks, 
technically  called  ' '  divisions  "  or  "  graduations  ' '  have 
been  cut  with  the  utmost  accuracy.  If  each  division 

represented  a 
degree  there 
would  be  360  of 
them  around 
the  entire  cir- 
cle. Usually 
there  is  a  grad- 
uation for  each 
five  minutes  of 
arc;  as  five  min- 
utes constitute 
one  twelfth  of  a 
degree,  there 
are  12x360,  or 
4,320  gradua- 
tions on  the 
circle. 
FIG.  79.— A  MERIDIAN  CIRCLE.  Jf  ^\\Q  tele- 

scope,  which  is  now  pointing  upward,  were  turned  so 
as  to  point  downward,  the  graduated  circle  would  turn 
with  it,  and  the  angle  through  which  the  telescope  was 
turned  could  be  measured  by  means  of  a  suitable  fixed 
pointer  placed  close  to  the  silver  graduations.  If  the 
pointer  were  opposite  the  10°  mark  on  the  circle  when 
the  telescope  was  pointing  directly  upward,  it  \vould  be 
opposite  the  mark  for  190°  when  the  telescope  pointed 

*  This  bearing  is  commonly  referred  to  as  a  "  wye." 


The  Astronomer' s  Workshop.  151 

straight  down,  the  circle  having  been  turned  just  half 
way  round.  Instead  of  one  pointer  there  are  usually 
four  ;  the  silver  graduations  are  so  fine  that  they  cannot 
be  well  seen  without  a  magnifying  glass  ;  the  pointer 
must  therefore  be  very  fine,  and  the  spider  is  called 
upon  to  furnish  it. 

The  spider-web,  which  is  to  serve  as  a  pointer,  is 
placed  inside  of  a  microscope,  which  is  sighted  at  the  The  reading 

0  ^  microscopes. 

silver  circle.  To  insure  great  accuracy  in  reading  the 
circle  four  microscopes  are  frequently  employed.  They 
are  shown  in  Fig.  79,  being  fastened  to  a  metal  drum, 
which  rests  on  top  of  one  of  the  piers.  On  looking 
through  one  of  the  microscopes  one  sees  the  spider- 
web,  and  also  the  magnified  divisions  on  the  circle.  At 
the  outer  end  of  each  microscope  a  little  box  is  placed  ; 
this  contains  a  measuring  instrument  called  a  microme- 
ter. If  the  spider-web  does  not  appear  to  coincide 
with  one  of  the  graduations  on  the  circle,  its  distance 
from  the  nearest  graduation  is  measured  with  the  mi- 
crometer. The  silver  circles  are  usually  read  to  the 
nearest  tenth  of  a  second  of  arc.  If  such  a  circle  be 
ninety  inches  in  circumference,  a  tenth  of  a  second  is 
only  TiiW  of  an  inch. 

Standing  upon  the  horizontal  axis  of  the  instrument  is  Thelevel 
a  metal  frame  which  supports  a  delicate  level,  the  sensi- 
tiveness of  which  is  astonishing.  Suppose  that  two 
points  on  the  level  tube,  one  eighth  of  an  inch  apart, 
are  in  the  same  horizontal  plane  at  a  given  instant.  If 
by  some  movement  of  the  instrument  one  of  the  points 
is  raised  a  millionth  of  an  inch  above  its  neighbor,  the 
level  bubble  will  move. 

A  peep  through  the  eyepiece  of  the  telescope  reveals 
a  forest  of  black  lines  ;  at  night,  when  lit  up  by  a  special 
lamp,  they  appear  as  a  system  of  golden  wires.  In  Fig. 


152 


A  Study  of  the  Sky. 


The  celestial 
meridian. 


A  surveyor's 
transit. 


80  are  nine  parallel  wires,  and  one  at  right  angles  to 
them.  Eight  are  arranged  symmetrically  with  respect 
to  the  middle  wire.  They  come  from  the  spider's  loom  ; 
woe  to  the  luckless  wight  who  accidentally  touches 
them,  or  blows  upon  them  !  They  are  in  the  focus  of 
the  telescope,  close  to  the  observer's  eye,  inside  of  the 
tube.  If  the  telescope  be  directed  to  the  heavens  on  a 
clear  night,  star  after  star  will  pass  through  the  field  of 
view,  marching  across  one  vertical  wire  after  another, 
moving  parallel  to  the  horizontal  wire. 

When  a  star  is  just  crossing  the  middle  wire,  it  is  on 
the  celestial  meridian  of  the  place  of  observation,  if  the 
instrument  is  in  perfect  adjustment.  Let  us  stop  a  mo- 
ment and  think  out  the  reason  why  a  star  is  on  the 

meridian  when  it  is  on 


\ 


this  middle  wire. 

Consider  a  surveyor's 
transit  which  he  carries 
about  and  sets  up  on 
its  tripod  whenever  he 
wishes  to  make  any 
measurements.  In  it 
there  are  two  cross 
wires,  one  horizontal, 
the  other  vertical.  If 
FIG.  so.— THK  SPIDER-WKBS.  he  wishes  to  sight  at  the 

top  of  a  church  spire  he  moves  his  telescope  until  the 
tip  of  the  spire  appears  to  lie  on  the  intersection  of  the 
cross  wires.  At  that  instant  a  straight  line  drawn  from 
the  top  of  the  steeple  through  the  center  of  the  object- 
glass  of  the  telescope  strikes  the  point  where  the  two 
wires  cross  each  other.  This  line  is  called  the  sight-line 
of  the  telescope. 

Returning  to  the  meridian  circle  we  see  that  its  sight- 


The  Astronomer1  s   Workshop. 


'53 


line,  which  is  a  line  drawn  from  the  center  of  the  object- 
glass  *  to  the  point  where  the  horizontal  and  central  ver- 
tical  wires  meet,  is  perpendicular  to  the  horizontal  axis. 
Let  us  point  the  telescope  at  some  house  miles  away  to 
the  southward.  Since  the  horizontal  axis  points  east 
and  west,  the  sight-line,  which  is  perpendicular  to  it, 
must  be  pointing  due  south.  If  a  chimney  of  the  house 
appears  to  lie 
upon  the  middle 
wire  the  chimney 
is  due  south  of 
the  instrument. 
Passing  by  the 
house  we  pro- 
long the  sight- 
line  to  the  celes- 
tial sphere,  which 
it  strikes  at  the 
south  point  of  the 
horizon. 

We  g  ently 

take  hold  of   the        FlG-  SI.—THE  SPIRE  ON  THE  CROSS  WIRES. 

telescope  and  pull  the  eye-end  down  ;  as  it  turns  on  the 
horizontal  axis  the  object-glass  rises,  and  the  sight-line 
traces  a  line  on  the  celestial  sphere.  Farther  and  far- 
ther upward  the  line  is  traced  on  the  sky  till  it  reaches 
the  zenith.  As  we  go  on,  the  circle  which  we  have 
been  tracing  runs  down  from  the  zenith  to  the  north 
point  of  the  horizon.  The  telescope  is  now  horizontal, 
and  pointing  northward.  We  continue  revolving  the 
telescope  in  the  same  direction  ;  the  eyepiece  rises  and 
the  object-glass  falls,  while  the  sight-line  is  cutting  into 
the  earth's  surface,  tracing  upon  it  the  terrestrial  merid- 

*  The  large  glass  at  the  upper  end  of  the  tube. 


The  telescope 
is  revolved. 


154 


A  Study  of  the  Sky. 


Mechanical 

perfection 

.sought. 


Perfection 
impossible. 


ian  of  the  place  of  observation.  When  the  telescope 
finally  reaches  its  original  horizontal  southward-pointing 
position,  the  sight-line  has  traced  the  celestial  meridian 
on  the  sky,  and  the  terrestrial  on  the  earth.  If  the 
celestial  meridian  were  visible  as  a  fine  gold  thread  lying 
on  the  celestial  sphere,  and  one  tried  to  look  at  it  with 
the  meridian  circle,  it  would  be  concealed  from  view, 
being  behind  the  central  spider-web.  Therefore,  at  the 
instant  when  any  star  appears  to  be  crossing  the  central 
spider-web,  it  is  on  the  meridian. 

Thus  far  we  have  considered  the  meridian  circle  as  an 
ideally  perfect  instrument.  True  it  is  that  the  mechan- 
ician has  exhausted  the  resources  of  his  art  when  he  has 
made  a  first-class  meridian  circle.  He  has  striven  to 
make  the  pivots  at  the  ends  of  the  axis  of  the  same  size 
and  exactly  round.  The  telescope  has  been  set  at  right 
angles  to  this  ;  the  object-glass  and  spider-webs  have 
been  inserted  with  the  utmost  care.  Upon  the  gradua- 
tions of  the  silver  circle  weeks  of  the  most  painstaking 
labor,  coupled  with  the  most  scrupulous  care,  have  been 
lavished.  The  microscopes  with  which  the  circle  is  read 
have  been  constructed  with  an  eye  to  perfection.  The 
interior  of  the  glass  level-tube,  which  is  to  test  the  hori- 
zontality  of  the  axis,  has  been  ground  to  the  proper 
curvature,  and  fastened  to  its  supporting  frame  in  such  a 
way  that  changes  of  temperature  will  not  cause  the  tube 
to  be  pinched  or  sprung.  The  mason  has  endeavored 
to  set  the  supporting  piers  so  solidly  that  nothing  short 
of  a  miniature  earthquake  will  disturb  their  positions. 

The  astronomer  views  the  finished  work  with  the  ad- 
miration which  every  one  must  have  for  any  piece  of 
mechanism  which  represents  the  utmost  of  human  skill. 
But  the  instrument,  which  is  to  the  eye  of  the  body  a 
thing  of  beauty,  is  to  the  mind  a  mass  of  imperfections. 


156 


A  Study  of  the  Sky. 


Flexure. 


Errors  of 
graduation. 


Level  errors. 


Movements  of 
the  ground. 


A  difficult  task. 


The  pivots  on  which  the  instrument  revolves  are  of 
unequal  sizes,  and  neither  of  them  is  round.  For  this 
reason  alone  the  sight-line,  instead  of  tracing  a  perfect 
circle  on  the  sky,  traces  a  gently  waving  line.  The 
axis,  which  is  apparently  amply  able  to  support  the 
light  telescope,  bends  a  trifle  under  its  weight  ;  per- 
chance one  half  of  it  bends  more  than  the  other  half. 
The  telescope  tube  flexes  under  the  weights  of  the 
object-glass  and  of  the  eye-end.  Changes  of  tempera- 
ture and  other  causes  alter  the  position  of  the  object- 
glass  in  its  cell,  and  change  the  direction  of  the  sight- 
line,  which  passes  through  its  center. 

The  exquisite  silver  circle  will  cost  the  astronomer 
many  a  month  of  arduous  toil.  For  if  he  assumes  that 
one  of  the  graduations  is  exactly  in  the  right  place, 
almost  all  of  the  remaining  4,319  are  so  far  out  of  their 
true  positions  that  he  must  determine  their  errors.  As 
we  have  before  stated,  he  wishes  to  read  as  small  a 
quantity  as  T?*W  of  an  inch,  and  most  of  the  circle- 
divisions  are  in  error  as  much  as  ^mnr  of  an  inch  ;  some 
of  them  are  over  swire  of  an  inch  out.  The  little  mi- 
crometers on  the  microscopes  cannot  do  their  small 
duties  with  sufficient  precision.  The  inner  surface  of  the 
level  tube,  which  has  been  ground  so  smooth,  is  embel- 
lished here  and  there  by  a  miniature  mountain,  which 
arrests  the  free  movement  of  the  level  bubble. 

The  solid  foundation  on  which  the  instrument  has 
been  set  is  continually  in  motion,  shifting  the  positions 
of  the  piers  by  small  amounts.  Earthquakes  are  only 
the  big  brothers  of  the  many  small  disturbances  of  the 
earth's  crust  which  are  noticed  by  astronomers  alone. 

The  observer  with  a  meridian  circle  has  therefore  a 
difficult  task  ;  he  must  manipulate  the  instrument  with 
exceeding  care,  and  must  study  many  of  its  errors  from 


The  Astronomer 's   Workshop. 


night  to  night,  because  they  continually  change  in  inex- 
plicable ways.  His  occupation  is  largely  an  unrelenting 
chase  after  errors,  which  must  be  determined  and  taken 
into  account. 

A  chronograph  is  considered  an  indispensable  part  of  A  chronograph, 
the  instrumental  equipment  of  an  observatory.  It  is 
used,  as  its  name  indicates,  for  noting  time.  At  any  in- 
stant when  an  observer  wants  to  note  the  time  he  touches 
a  telegraph  key,  and  the  chronograph  records  the  time. 
The  large  cylinder  shown  in  Fig.  83  revolves  once  a 
minute.  If  the  pen-carriage  stood  still  the  pen  would 


FIG.  83.— A  CHRONOGRAPH. 

draw  the  same  circle  over  and  over  again  on  the  paper 
which  is  wrapped  around  the  cylinder.  But  the  mech- 
anism is  so  arranged  that  the  pen-carriage  slides  slowly 
from  one  end  of  the  cylinder  to  the  other.  The  pen 
therefore  traces  upon  the  paper  a  long  spiral  line,  like  a 
screw-thread.  When  a  telegraph  operator  presses  his 
telegraph  key  the  sounder  by  his  side  clicks.  If  a  pen 
were  suitably  attached  to  the  sounder,  the  pen  would 
make  a  mark  on  paper.  In  a  similar  fashion  a  notch  is 
made  in  the  line  which  the  pen  draws  on  the  chrono- 
graph sheet,  whenever  an  observer  presses  the  key. 


The  pen- 
carriage  slides. 


158 


A  Study  of  the  Sky. 


The  record  of 
the  clock. 


The  time  noted. 


The  microm- 
eter. 


The  clock  is  equipped  with  a  little  device  which  acts 
like  an  automatic  telegraph  key,  causing  the  pen  on  the 
chronograph  to  make  a  notch  whenever  the  clock  ticks, 
with  the  exception  of  the  fifty-ninth  second  of  each 
minute,  for  which  there  is  no  record  on  the  chronograph. 
The  omission  of  this  second  is  a  matter  of  convenience, 
to  identify  the  beginning  of  each  minute.  If  the  ob- 
server notices  the  time  when  one  of  the  clock  notches 


FIG.  84.— A  PORTION  OF  A  CHRONOGRAPH  SHEET. 

was  made,  he  can  easily  tell  what  the  clock  read  when 
any  other  notch  was  made. 

When  he  sees  a  star  cross  a  spider-web  in  the  meridian 
circle  and  touches  his  key,  a  notch  is  made  which 
usually  comes  between  two  of  the  clock  notches.  If  it  is 
between  the  notches  for  ghr-  28min-  3sec-  and  9hr-  28min'4sec-, 
the  fractional  part  of  a  second  is  estimated  from  the  rel- 
ative distances  between  the  notches.  One  of  the  notches 
shown  in  Fig.  84  was  evidently  made  at  9hr-  28min-  3.4sec- 
It* is  much  easier  for  an  observer  to  touch  a  telegraph 
key  at  the  proper  instant  than  to  estimate  the  required 
time  by  listening  to  the  ticks  of  a  clock,  while  his  eye  is 
occupied  at  the  eyepiece  of  the  telescope. 

The  micrometer  is  used  on  all  kinds  of  astronomical 
instruments  wherever  small  distances  are  to  be  measured 
accurately.  It  aids  in  reading  the  silver  circle  on  a 
meridian  circle  ;  the  diameters  of  planets,  the  heights  of 
mountains  on  the  moon,  and  the  distances  of  the  stars 
are  all  measured  by  its  help.  It  is  beyond  our  present 
province  to  explain  how  the  minute  fractions  of  an  inch 
which  a  micrometer  measures  are  transmuted  into  miles 
in  the  celestial  spaces,  by  the  alchemy  of  the  mathema- 


The  Astronomer 's    Workshop.  159 

tician's  art.  But  we  may  at  least  see  what  the  great 
micrometer  which  is  screwed  on  at  the  eye-end  of  the  . 

J  micrometer. 

Lick  telescope  looks  like,  and  get  a  little  insight  into  the 
method  of  its  manipulation.  Looking  through  the  eye- 
piece, we  shall  not  be  confronted  by  a  forest  of  spider- 
webs,  as  in  the  meridian  circle.  It  will  suffice  if  there 
are  but  two  fixed  wires  crossing  each  other  at  a  right 
angle,  just  as  in  the  surveyor's  transit.  Besides  the  fixed 


FIG.  85. — THE  LICK  MICROMETER. 

wires  there  must  be  one  movable  one,  which  is  parallel 

to  one  of  the  fixed  wires.     The  concealed  frame,  which 

holds  the  movable  wire,  is  driven  by  a  fine  screw,  the  A  fine  screw. 

large  head  of  which  is  visible  at  one  end  of  the  box.    This 

head  is  graduated  so  that  thousandths  of  a  revolution  of 

the  screw  can  be  read.      If  the  screw  has  fifty  threads  to 

the  inch,  an  entire  revolution  of  it  will  cause  the  movable 

spider-web  to  move  y&  of  an  inch.     One  hundredth  of  a 

revolution  will  cause  a  motion  of  -jo1™  of  an  inch. 


i6o 


A  Study  of  the  Sky. 


A  planet's 
diameter. 


C//SC. 


Distance 
between  stars. 


If  the  diameter  of  a  planet  is  to  be  measured,  the 
movable  spider-web  is  driven,  by  turning  the  screw, 
until  the  image  of  the  planet  in  the  field  of  view  is  neatly 

embraced  be- 
tween the  two 
parallel  spider- 
webs.  The  read- 
ing of  the  gradu- 
ated head  of  the 
micrometer  screw 
is  taken,  and  the 
solution  of  the 
problem  is  then  a 
mere  matter  of  a 
little  simple  fig- 
uring, which  the 
astronomer  does 
at  his  leisure. 

When  the  ap- 
parent distance 
between  two  stars 
is  to  be  meas- 
ured, the  mi- 
crometer box, 
containing  the 
spider-webs,  is 
turned  till  the 
two  parallel  webs 
stand  perpendic- 
ular to  a  line 

FIG.  86. — MEASUREMENT  OF  A  PLANET'S  DIAMETER,    joinin0"   the  Stars. 

At  the  completion  of  the  measure  the  spider-webs  are 
bisecting  the  images  of  the  stars,  as  shown  in  Fig.  87. 
In  reducing  observations  made  with  the  micrometer 


The  Astronomer1  s  Workshop. 


161 


no  such  tantalizing  chain  of  errors  is  encountered  as 
with  the  meridian  circle.  If  the  micrometer  screw  were  Errors, 
of  even  pitch  throughout  its  length,  so  that  each  revolu- 
tion of  it  advanced  the  spider-web  just  -fa  of  an  inch,  all 
would  be  well.  When  the  irregularities  in  the  screw- 
pitch,  which  are  always  very  small,  have  been  deter- 
mined, the  battle  is  won. 

If,  however,   one  of  the  spider-webs  is 
accidentally  broken,  the  insertion  of  a  new 
one  demands  a  little  skill.     The  astrono- 
mer cannot  sweep  down  one  of  the  cob- 
webs in  the  observatory  to  get  a  suitable 
wire.     House-spiders  are  too  effeminate ; 
their  webs  are  not  sufficiently  tough,  and 
are  covered  with  dust.     A  big  field-spider, 
which  successfully  copes  with  an  unwary 
grasshopper,  binding  his  struggling  victim 
by  weaving  a  shroud  about  him,  produces 
a  web  that  is  elastic  and  tenacious.     The 
cocoon,  in  which  are  stored  hundreds  of 
yards  of  gauzy  fiber,  is  captured.      By  the 
exercise  of  a  little  dexterity  a  piece  of  web 
three  or  four  inches  long  is  pulled  out  and 
placed    under    a    magnifying    glass.       It 
proves  to  be  too  thick,   and  is  rejected. 
Another  piece  is  examined  ;  curious  little 
knots  are  strung  along  it.     The  next  piece,  Fl'G.87._BlSECTION 
when  held  up  to  the  light,  is  too  transpar-    BY  SPIDER-WEBS. 
ent.     Soon  a  fine,  smooth,  opaque  bit  of  web  is  discov- 
ered ;  it  is  submerged  in  a  basin  of  water  and  stretched 
out,  while  soaking,  so  that  it  becomes  finer  yet.      Inside 
of  the  micrometer  are  two  fine  grooves.     One  end  of  the 
web  is  laid  in  its  groove,  with  the  aid  of  a  magnifying 
glass,  and  a  drop  of  shellac  is  dropped  upon  it ;    the 


A  broken 
spider-web. 


162 


A  Study  of  the  Sky, 


The  spectro- 
scope. 


A  shower. 


shellac  hardens  and  holds  it.  It  is  now  stretched  taut 
with  the  utmost  care,  and  the  other  end  fastened  in  its 
groove  ;  if  it  be  not  pulled  with  sufficient  force,  it  will 
be  baggy  and  useless.  If  pulled  a  trifle  too  hard,  all  is 
over  in  an  instant,  and  the  cocoon  is  explored  for  a  new 
web. 

One  more  instrument  demands  attention.  It  is  the 
wonder-working  spectroscope,  with  which  substances 
which  exist  in  distant  stars  are  detected,  and  motions 
otherwise  unknown  are  brought  to  light. 

White  light  is  a  combination  of  many  different  colors. 
When  the  sun  shines  through  a  shower  of  rain,  his  light 


Construction 
of  the  spectro- 
scope. 


FIG.  88. — ESSENTIALS  OF  A  SPECTROSCOPE. 

is  split  up  in  passing  through  the  raindrops,  and  a  rain- 
bow is  produced.  Many  an  old  lamp,  once  the  glory 
of  grandfather's  parlor,  is  surrounded  by  prismatic 
pieces  of  glass,  which  are  rich  with  varied  hues,  as  the 
light  shines  through  them  and  is  dispersed  into  its 
component  colors. 

The  spectroscope  is  a  beautiful  instrument,  in  which 
the  light  is  dispersed,  and  by  which  it  is  studied. 
Fig.  88  shows  a  triangular  prism  of  glass,  on  each  side 
of  which  a  telescope  is  placed.  The  eyepiece  of  the 


The  Astronomer1  s  Workshop.  163 

telescope  at  the  right  has  been  supplanted  by  a  brass 
cap,  in  which  there  is  a  long  narrow  slit.  The  light 
from  an  ordinary  lamp  enters  at  this  slit,  impinges  upon 
the  prism,  is  dispersed  by  the  prism,  enters  the  telescope 
at  the  left,  and  emerges  into  the  observer's  eye. 

The  light  which  entered  the  narrow  slit  has  been 
spread  out  into  a  ribbon  which  is  red  at  one  end  and 
violet  at  the  other.  Between  these  colors  lie  orange, 
yellow,  green,  cyan-blue,  and  ultramarine  blue.  The 
ribbon  is  called  a  spectrum. 

Let  us  now  replace  the  lamp  by  a  spirit  lamp,  and  lay  Ex  eriments 
some  common  salt  on  the  wick.  The  previously  color- 
less flame  becomes  yellow,  as  the  salt  burns.  Looking 
into  the  spectroscope  we  see  no  longer  a  colored  band, 
but  simply  a  yellow  line.  When  the  salt  has  been 
burned  up  we  try  chloride  of  lithium  in  the  same  way  ; 
a  carmine  line  appears.  A  salt  of  thallium  will  produce 
a  green  line.  Burn  all  the  substances  together,  and  all 
the  lines  are  visible  simultaneously. 

Again  let  us  look  at  the  yellow  line,  as  the  salt  is 

Further 

being  turned  from  a  solid  into  a  gas,  in  the  hot  flame  of  experiments. 

the  spirit  lamp.     Behind  the  spirit  lamp  is  put  a  very 

bright  white  light,  which  will  shine  through  the  hot  gas 

into  the  slit.     In  place  of  the  bright  line  produced  by 

the  glowing  yellow  gas  there  is  now  a  dark  line,  and  on 

either  side  of  it  the  spectrum  stretches  in  all  its  beauty, 

violet  at  one  end,  red  at  the  other.     The  dark  line  lies 

in  that  part  of  the  spectrum  which  is  of  a  yellow  color. 

If  the  spirit  lamp  be  now  removed,  the  dark  line  in  the 

yellow  of  the  spectrum  disappears,  and  the  spectrum  is, 

as  at  first,  a  variously  colored  ribbon,  in  which  there  are 

no  dark  lines.     What  caused  the  dark  line,  which  has 

now  vanished  ?     The  bright  white  light  is  composed  of 

all  sorts  of  colors,  among  which  is  yellow.     When  this 


164 


A  Study  of  the  Sky. 


Three  prin- 
ciples. 


The  principles 
applied. 


light  shone  through  the  hot  yellow  gas  in  the  spirit- 
flame,  the  gas  absorbed  some  of  it,  so  that  there  was  a 
dark  place  in  the  yellow  of  the  spectrum. 

By  numerous  experiments  the  following  principles 
have  been  established  : 

Principle  I.  An  incandescent  solid  or  liquid,  or  a 
glowing  gas  which  is  made  dense  by  the  application  of 
pressure,  produces  a  spectrum,  which  is  a  ribbon  of  light 
of  various  colors,  as  previously  described.  This  is  a 
continuous  spectrum. 

Principle  II.  A  heated  gas,  which  is  composed  of 
only  one  chemical  element,  gives  a  spectrum  consisting 
of  one  or  more  bright  lines.  This  is  a  bright-line 
spectrum. 

Principle  III.  A  white  light  shining  through  a  gas 
produces  a  spectrum  which  would  be  continuous  if  it 
were  not  crossed  by  dark  lines.  The  dark  lines  cor- 
respond in  position  to  the  bright  lines  in  the  spectrum 
of  the  gas.  This  is  a  reversed  spectrum. 

How  does  an  astronomer  apply  these  principles? 
He  takes  off  the  eye-end  of  his  telescope,  and  attaches 
the  spectroscope  instead.  The  instrument  is  directed 
at  a  nebula  ;  the  light  from  the  nebula  enters  the  spec- 
troscope slit,  passes  through  the  prism,  and  produces  a 
spectrum  of  bright  lines.  The  nebula  is  therefore  a 
glowing  gas.  By  comparing  the  spectrum  of  the  nebula 
with  the  spectrum  of  hydrogen,  for  instance,  it  is  proven 
that  hydrogen  is  present  in  the  nebula. 

The  spectrum  of  the  sun  is  a  reversed  spectrum 
crowded  with  thousands  of  dark  lines.  White  light 
coming  from  the  sun's  interior  passes  through  the 
heated  gases  in  his  atmosphere,  and  suffers  absorption, 
according  to  Principle  III.  A  spectroscope  can  be  so 
constructed  that  the  spectrum  of  the  vapor  of  sodium 


The  Astronomer' s  Workshop.  165 

will  be  shown  in  the  field  of  view,  just  below  the  solar 
spectrum.  The  prominent  lines  in  the  sodium  spectrum 
are  just  below  certain  dark  ones  in  the  solar  spectrum. 
Sodium  is  therefore  in  the  sun. 

What  would  the  observer  conclude  about  the  nebula 
in  Andromeda  if  its  spectrum  were  continuous  ? 

Powerful  spectroscopes  are  provided  with  more  than 
one  prism,  and  are  too  complicated  to  be  explained 
easily. 

For  certain  classes  of  work  prisms  are  rejected,  their  Agrating 
place  being  taken  by  a  diffraction  grating,  which  is  a 


FIG.  89.— A  SPECTROSCOPE. 

metallic  mirror  on  the  face  of  which  thousands  of  fine 
lines  have  been  ruled.  Sometimes  40,0x30  lines  are 
ruled  side  by  side  in  a  space  an  inch  wide.  White  light 
is  dispersed  into  its  different  colors  by  being  reflected 
from  the  surface  of  the  grating. 

There  are  many  other  astronomical  tools,  descriptions   Photography 
of  which  are  forbidden  by  the  limitations  of  this  book. 
Mention  must  however  be  made  of  the  photographer's 
camera,  which  is  so  common  a  piece  of  apparatus  that  a 
description  of  it  is  unnecessary.      Many  special  photo- 


1 66  A  Study  of  the  Sky. 

graphic  telescopes  have  been  built,  which  have  revealed 
objects  too  faint  to  be  seen  with  the  most  powerful 
visual  telescopes.  To  the  results  of  photographic  work 
in  various  astronomical  lines,  reference  will  be  made 
from  time  to  time.  Very  many  departments  of  observa- 
Superiorre-  tional  astronomy  have  been  invaded  by  the  sensitive 
plate,  which,  despite  its  imperfections  and  limitations,  is 
now  admitted  to  -furnish  results  superior  to  those 
obtained  without  its  aid. 


CHAPTER  X. 

TIME. 

' '  Old  Time,  in  whose  bank  we  deposit  our  notes, 
Is  a  miser  who  always  wants  guineas  for  groats  ; 
He  keeps  all  his  customers  still  in  arrears 
By  lending  them  minutes  and  charging  them  years." 

— Holmes. 

IN  this  busy  age,  when  more  progress  is  made  in  a 
minute  than  was  formerly  made  in  an  hour,  and  the  importanceof 
exacting  demands  upon  men  in  all  walks  of  life  make  accurate  time- 
them  more  chary  of  hours  than  their  forefathers  were  of 
days,  the  importance  of  accurate  time  is  realized  as 
never  before.  The  piercing  whistle  of  the  factory  or 
machine  shop  wakes  the  echoes  of  the  early  morning 
at  the  exact  moment  when  some  steady  clock  reads 
seven,  and  hundreds  of  working  people  take  their  places 
promptly,  to  begin  the  day's  toil.  The  railroad  con- 
ductor, with  pocket  chronometer  in  his  hand,  stands 
beside  the  palatial  through  train,  while  the  engineer 
holds  the  panting  locomotive  in  check,  till  the  signal  is 
given  to  open  the  throttle  and  speed  the  waiting  pas- 
sengers on  their  way. 

"Thirty  seconds  too  late,"  says  the  depot  clock,  as 
the  belated  traveler  hurries  to  the  platform,  only  to  TardyPe°Ple- 
find  that  the  train  has  pulled  out.  (<  Our  clock  at  home 
was  five  minutes  slow,"  says  the  blushing  schoolgirl, 
when  called  to  account  for  her  tardiness.  '  *  The  school 
clock  must  be  a  minute  and  a  half  too  fast,"  says  the 
boy  who  played  marbles  two  minutes  too  long.  The 


168 


A  Study  of  the  Sky. 


A  wreck. 


Small  fractions. 


Standard  time. 


Time  obser- 
vations. 


business  man  paces  impatiently  to  and  fro  in  his  office, 
waiting  for  friends  who  were  to  come  precisely  at  three. 
The  electric  car  has  just  gone  by,  and  the  mistress  of 
the  house,  arrayed  for  an  afternoon's  shopping,  stands 
on  her  doorstep  in  a  pet ;  the  kitchen  clock  was  two 
minutes  slow.  The  careful  mariner,  feeling  his  way 
along  the  coast,  through  a  fog,  feels  a  shock  which 
shows  that  the  good  ship  has  struck  a  rock.  The 
trusted  chronometer  has  gone  wrong,  and  the  ship  must 
go  down  in  the  seething  floods. 

Scientists  dispute  about  tenths  of  seconds,  quibble 
over  hundredths,  and  take  still  smaller  fractions  into 
account,  while  the  world  wonders  how  they  contrive  to 
measure  intervals  of  time  so  minute. 

Though  all  the  daily  doings  of  the  civilized  world  are 
governed  to  a  large  extent  by  the  timekeepers  which 
are  to  be  found  everywhere,  few  stop  to  inquire  into  the 
authoritative  source  of  standard  time,  and  the  methods  of 
its  dissemination.  People  generally  have  vague  notions 
that  astronomers  observe  the  sun  when  it  is  on  the 
meridian,  regulate  their  clocks  accordingly,  and  then 
telegraph  the  time  about  for  the  benefit  of  railroads  and 
jewelers. 

Let  us  go  to  the  bottom  of  this  matter,  by  visiting 
an  observatory  and  seeing  just  what  the  astronomer 
does  ;  we  must  not  go  at  mid-day,  for  he  does  not  use 
the  sun  to  get  time  by.  In  the  evening  we  may  find 
him  at  work,  and  fortunate  shall  we  be  if  he  permits  us 
to  sit  down  in  the  room  where  he  is  observing,  and 
silently  watch  his  operations.  In  the  center  of  the  dimly 
lighted  room  is  the  meridian  circle,  which  we  have 
described  in  Chapter  IX.  The  roof  shutters  have  been 
opened,  and  we  may  see  the  stars  trooping  past  on  their 
way  to  the  western  horizon.  On  a  table  near  the 


Time.  169 

instrument  stands  a  chronometer,  ticking  off  each  half 
second  ;  by  its  side  lies  a  book,  containing  a  list  of  stars. 
The  book  gives  the  right  ascension  and  declination  of 
each  star.  The  astronomer  glances  at  his  chronometer 
and  sees  that  its  reading  is  about  8hr-  53min-  In  the  list 
he  finds  a  star  whose  right  ascension  is  8hr-  56min- 
4-93sec'  The  star  therefore  will  cross  his  meridian  about 
ghr.  E^min^  ancj  w{\\  COme  into  the  field  of  view  of  his 
instrument  a  few  seconds  before  that  time. 

Looking  at  the  declination  he  mentally  figures  out  the 
reading  of  the  silver  circle,  when  the  telescope  has  the  set. 
proper  slant  to  the  horizon.  In  a  minute  he  has  turned 
the  telescope  on  its  horizontal  axis  till  the  circle  has  the 
proper  reading,  and  has  applied  his  eye  at  the  eyepiece. 
Faint  stars  come  drifting  through  the  field  of  view, 
shying  past  the  golden  spider-webs,  as  if  they  wished  to 
escape  from  the  astronomer's  gaze  as  quickly  as  pos- 
sible ;  but  he  pays  no  attention  to  them. 

In  a  short  time  the  expected  bright  star  appears  on 
the  edge  of  the  field  of  view,  glowing  like  a  little  sun.  The  star  comes' 
The  observer  glances  quickly  at  the  chronometer,  and 
begins  counting  the  readings  of  the  second-hand  ; 
"four,  half,  five,  half,  six,  half,"  he  says  to  himself,  as 
he  resumes  his  place  at  the  eyepiece.  The  star  moves 
onward  ;  it  has  leaped  across  the  first  spider-web,  and 
the  astronomer  hurriedly  writes  in  his  note-book  the 
figures  13.1. 

He  has  estimated  that  the  star  crossed  the  first  spider- 
web  one  tenth  of  a  second  after  the  chronometer  ticked  mates?  e 
the  thirteenth  second  of  some  minute.  Hurriedly  glanc- 
ing at  the  chronometer's  face  he  again  counts,  and  after 
a  few  seconds  he  makes  another  record,  perchance  24.7. 
Thus  he  continues  till  the  star  has  crossed  the  last 
spider-web  ;  having  gotten  the  seconds  and  fractions  of 


1 7o 


A  Study  of  the  Sky. 


The  chronom- 
eter's error. 


Personal 
equation. 


a  second  as  correctly  as  he  can,  he  writes  down  the 
minute  and  the  hour  more  leisurely.  The  record  stands 
as  follows  : 

13.1**- 

24.7 

33-6 

42.4 

ghr.   55min.   ^^ 

The  average  of  these  five  times,  obtained  by  dividing 
their  sum  by  5,  is  8hr-  55™"-  33-58sec-  That  is  the 
time,  as  nearly  as  the  astronomer  could  estimate  it, 
which  the  chronometer  read  when  the  star  crossed  his 
meridian.  The  book  on  the  table  states  that  the  star 
really  crossed  the  meridian  at  8hr-  56™"-  4-93sec- 

The  chronometer  must  therefore  be  in  error  ;  by  sub- 
tracting the  chronometer  time  from  the  time  given  in 
the  book,  we  get  the  remainder  3i.35sec>  Shall  we  not 
say  that  the  chronometer  is  3i-35sec-  slow?  If  the 
observer  could  estimate  the  time  when  the  star  crossed 
each  spider-web  accurately,  and  the  instrument  were 
perfectly  adjusted  in  the  meridian,  one  star  would  be 
sufficient.  But  the  instrument  has  many  errors,  which 
must  be  taken  into  the  reckoning,  and  the  observer  can- 
not do  anything  as  accurately  as  he  wishes.  He  there- 
fore observes  several  stars,  and  applies  the  refinements 
of  mathematical  analysis  to  the  problem  in  order  to 
determine  the  errors  of  the  instrument,  and  make 
allowance  for  them.  From  the  observation  of  each  star 
he  obtains  a  value  of  the  error  of  the  chronometer  ; 
these  he  combines,  taking  their  average  as  the  final 
result. 

When  the  utmost  obtainable  accuracy  is  desired,  the 
' '  personal  equation  ' '  of  the  observer  must  be  taken  into 
account.  It  takes  time  for  men  to  think  ;  the  more 


Time.  1 7 1 

complicated  the  operation,  the  greater  the  time.  In 
the  case  of  eye  and  ear  observations,  such  as  have 
just  been  described,  one  impression  reaches  the  brain 
through  the  eye,  when  the  star  crosses  the  wire. 
Another  impression  conies  from  the  chronometer,  and 
is  transmitted  by  way  of  the  ear.  The  brain  is  occupied 
with  the  process  of  counting,  but  when  the  two  impres- 
sions arrive,  it  compares  them,  pronounces  judgment, 
and  directs  the  hand  to  make  a  certain  record.  If  a 
man  is  especially  trained  he  can  do  all  this  without 
losing  his  count  of  the  chronometer-beats.  He  can 
even  observe  the  times  of  transit  across  two  or  three 
wires  without  removing  his  eye  from  the  eyepiece,  or 
stopping  to  write  anything  down. 

In    the   case   of    chronographic   observations,    which  Chronographic 
have  been  described  in  Chapter  IX. ,  and  which  are  now   observations, 
generally  used,    the  brain    has  much   less  to  do.     As 
before  it  receives  an  impression  by  way  of  the  nerves  of 
sight,  and  sends  a  mandate  to  the  finger  to  touch  the 
telegraph  key.     The  mandate  is  obeyed,  and  the  time 
is  recorded  almost  instantaneously  on  the  chronograph 
sheet.     The  personal  equation  for  eye  and  ear  observa- 
tions   is  usually  greater  than    for  chronographic  work, 
because  of  the  greater  complexity  of  the  process. 

A  machine   has   been   invented   for  determining  the 
personal  equation   of   a  time  observer.     The  observer 

Personal 

looks  through  a  little  tube,  resembling  the  eyepiece  of  a  equation 

./.    .   i  i  •    i      •       i    •  machine. 

telescope,  and  sees  an  artificial  star,  which  is  driven  by 
clockwork  across  a  system  of  wires.  The  machine 
automatically  records  the  time  when  the  star  crosses 
each  wire  ;  the  astronomer  presses  his  telegraph  key, 
as  usual,  and  thus  records  the  time  when  he  thinks  that 
the  star  crosses  each  wire. 

Such    tests    have    demonstrated     that    the    average 


172 


A  Study  of  the  Sky. 


observer  is  between  one  and  two  tenths  of  a  second 
behind  time.  Sometimes  he  has  a  habit  of  touching  the 
key  a  few  hundredths  of  a  second  before  the  star  reaches 
the  wire  ;  he  probably  estimates  the  rate  at  which  the 
star  is  moving,  and  starts  his  mental  machinery  ahead  of 
time,  endeavoring  to  get  the  nervous  impulse  down 
to  his  finger  at  the  time  when  the  star  arrives  at  the 
wire.  In  the  case  of  eye  and  ear  observations  a  discrep- 
ancy of  over  a  second  was  once  found  between  two 
noted  astronomers  ;  the  cause  of  so  large  a  difference 
can  only  be  guessed  at.  Apart  from  personal  equation, 
Probable  error,  the  probable  error  of  a  time  determination  derived  from 
a  dozen  stars  is  two  or  three  hundredths  of  a  second. 

Time,  like  money,  is  easier  to  get  than  to  keep. 
After  the  error  of  a  clock  has  been  found,  its  rate  must 
be  sought.  If  on  January  8,  at  7  p.  m. ,  a  clock  is 
io.93sec- fast,  and  on  January  n,  at  7  p.  m.,  another 
series  of  observations  makes  its  error  io.42sec-  fast,  it 
has  lost  o.5isec-  in  three  days  and  is  therefore  losing 
o.  i7sec-  a  day.  This  rate  is  used  in  predicting  the  error 
for  a  few  days  ahead.  If  one  wishes  to  know  the  error 
on  January  13  at  7  p.  m.,  he  computes  that  the  loss  in 
two  days  is  2x0.  i7sec-,  which  equals  o.  34sec- ;  since  the 
clock  was  io.42sec-fast  on  January  1 1,  and  has  since  lost 
o.34sec-,  it  must  be  only  io.o8sec-  fast.  But  the  rate  can 
be  relied  upon  for  only  a  few  days  ;  the  clock  may  be  as 
fine  as  the  maker  can  produce  ;  it  may  be  enclosed  in 
an  air-tight  case,  so  that  variations  in  the  pressure  and 
humidity  of  the  air  have  no  appreciable  effect  upon  it ; 
it  may  be  put  upon  as  solid  a  base  as  can  be  found,  and 
in  a  room  kept  at  as  constant  a  temperature  as  possible  ; 
it  may  be  wound  by  an  electric  motor,  so  that  the  case 
need  not  be  opened — yet  its  performance  will  not  satisfy 
the  astronomer.  Week  after  week  its  rate  will  change 


Error  and  rate. 


Time.  173 

by  small  amounts,  from  obscure  causes,  which  the 
astronomer  cannot  even  foresee.  Over  and  over  again 
must  observations  be  made,  and  calculations  be  carried 
through,  that  the  time  may  be  well  kept. 

No  endeavor  is  made  to  keep  a  standard  clock  right, 
for  the  constant  changes  which  would  be  necessary 
would  introduce  intolerable  disturbances  into  the  clock's 
performance.  It  is  therefore  permitted  to  go  on  month 
after  month,  without  alteration,  its  errors  and  rates 
being  determined  from  time  to  time  by  observations  of 
the  stars. 

We  have  seen  how  an  astronomer  gets  time,  and  how 
he  endeavors  to  keep   it.     We  shall  now  see  how  he  nated> 
disseminates  it  for  the  benefit  of  the  country  at  large. 

Here  electricity  comes  into  play  ;  as  a  telegraph 
operator  by  touching  his  key  can  make  any  sounder  on 
the  line  tick,  so  a  clock  may  be  arranged  to  accomplish 
the  same  end.  While  the  second-hand  is  flying  from 
one  second  to  the  next  one,  a  tooth  of  a  wheel  mounted 
on  the  same  arbor  as  the  second-hand  strikes  a  miniature 
telegraph  key,  and  the  signal  is  sent.  One  of  the  clocks 
at  the  United  States  Naval  Observatory  at  Washington 
sends  a  signal  over  the  Western  Union  wires  to  distant 
cities  day  after  day,  and  thousands  of  telegraphic  instru- 
ments tick  as  the  signal  passes. 

The  sending  of  the  signal  is  but  a  small  part  of  the  c 

*>  7  .  .  Special  devices. 

work  of  disseminating  the  time.  In  some  cities  a  time 
ball  is  hoisted  to  the  top  of  a  pole  a  few  minutes  before 
noon,  and  released  at  noon  by  an  electrical  impulse.-  In 
others  the  fire  bells  are  rung  at  the  same  hour.  The 
Western  Union  Telegraph  Company  controls  a  system 
of  clocks,  which  are  set  automatically  once  a  day,  when 
a  signal  is  sent  to  them.  Thus  a  business  man  may 
have  reasonably  correct  time  in  his  office,  if  he  is  willing 


A  Study  of  the  Sky. 


Standard 
meridians. 


Improvements 
in  the  plan. 


to  pay  the  small  rental  charged  by  the  company.*  The 
system  conduces  to  the  accurate  running  of  trains,  for 
every  important  railway  station  contains  a  telegraph  office. 

The  system  of  standard  meridians,  which  has  been 
adopted  by  the  railroads  and  by  the  most  important 
municipalities,  is  a  great  convenience.  The  trains  in 
the  eastern  portion  of  the  United  States  are  governed 
by  Eastern  Standard  time,  which  is  five  hours  later  than 
Greenwich  time,  and  is  not  far  from  local  time  at  Phila- 
delphia. Central  Standard  time  is  six  hours  later  than 
Greenwich  time,  and  is  used  in  the  Mississippi  Valley 
and  adjacent  states.  It  is  nearly  the  same  as  local  time 
at  St.  Louis.  Mountain  time  differs  from  Greenwich 
time  by  seven  hours,  and  dominates  the  semi-arid  region 
formerly  known  as  the  Great  American  Desert.  The 
seven-hour  meridian  passes  through  Denver.  Pacific 
time,  one  hour  slower  still,  is  the  standard  for  the 
Pacific  coast.  The  eight-hour  meridian  passes  centrally 
through  California. 

Two  further  improvements  upon  this  plan  may  yet  be 
made.  There  should  be  no  insurmountable  difficulty  in 
having  the  time  the  same  throughout  any  given  state. 
The  fact  that  the  meridian  by  which  Central  time  is 
governed  runs  near  the  Mississippi  River  much  facili- 
tates the  grouping  of  the  states  in  such  a  way  that  the 
time  which  should  be  adopted  in  each  one  is  easily 
remembered,  f 

*  The  clocks  furnished  are  of  a  fair  grade,  and  are  expected  to  vary  only  a 
few  seconds  a  day.  They  are  set  just  right  by  the  signal,  and  if  they  do  not 
get  out  more  than  twenty  seconds  during  the  ensuing  twenty-four  hours,  the 
next  signal  sets  them  right  again.  A  rate  of  twenty  seconds  a  day  is  rare. 
The  system  has  therefore  a  high  efficiency. 

t  Central  Standard  time  should  be  in  force  in  all  the  states  which  border  on 
the  Mississippi,  and  the  three  great  lakes,  Superior,  Michigan,  and  Huron, 
together  with  Alabama.  These  states  are  Michigan,  Indiana,  Kentucky, 
Tennessee,  Alabama,  Wisconsin,  Illinois,  Mississippi,  Missouri,  Arkansas,  and 
Louisiana. 

Eastern  time  should  be  the  standard  in  all  states  east  of  the  preceding  ones. 
These  are  Maine,  New  Hampshire,  Vermont,  Massachusetts,  Rhode  Island, 


Time.  175 

A  further  desirable  change,  which  would  be  more 
difficult  of  accomplishment,  because  of  the  conservatism 
of  even  so  progressive  a  people  as  Americans,  is  count- 
ing the  hours  continuously  through  the  day  from  one  to 
twenty-four.  The  designations,  a.  m.  and  p.  m.,  would 
then  be  unnecessary.  This  system  has  already  been 
tried  upon  the  Canadian  Pacific  Railway,  and  is  in  force 
in  Italy.  Its  advantages  are  simplicity  and  accuracy. 
Astronomers  already  have  a  twenty-four-hour  day, 
which  begins  at  noon. 

The  business  man  prefers  to  have  the  date  change  at  Astronomical 
midnight,  when  he  is  usually  asleep.  The  astronomer  and  civil  date, 
finds  it  inconvenient  to  change  the  date  at  midnight, 
when  he  is  frequently  engaged  in  observation.  The 
astronomical  day  begins  twelve  hours  later  than  the  civil 
day  ;  January  5,  10  a.  m.,  is  January  4,  22  hours,  by 
astronomical  reckoning.  March  16,  8  p.  m.,  is  March 
1 6,  8  hours,  astronomically  reckoned.  Astronomers 
have  of  late  years  discussed  the  advisability  of  making 
their  day  begin  at  the  same  time  as  the  civil  day,  viz. , 
at  midnight,  but  they  have  not  yet  made  the  change. 

Europe  is  much  in  advance  of  America  in  the  matter 
of  time  distribution.  The  city  of  Paris  is  supplied  with  Europe, 
a  system  of  electrical  clocks,  and  also  with  a  system  of 
pneumatic  clocks,  which,  as  their  name  indicates,  are 
driven  by  compressed  air.  The  standard  clocks  are  so 
numerous  that  any  one  may  learn  the  time  accurately, 
with  little  trouble.  Many  small  municipalities  have 
extensive  systems  of  electrical  dials. 


Connecticut,  New  Jersey,  Maryland,  the  Virginias,  the  Carolinas,  Georgia, 
Florida,  New  York,  Pennsylvania,  and  Ohio. 

Mountain  time  should  prevail  in  the  first  double  row  of  states  and  territories 
west  of  the  states  which  have  Central  time.  These  are  the  Dakotas,  Nebraska, 
Kansas,  Indian  Territory,  Oklahoma,  Texas,  Montana,  Wyoming,  Colorado, 
and  New  Mexico. 

Pacific  time  should  be  adopted  by  all  the  remaining  states.  These  are 
Idaho,  Utah,  Arizona,  Washington,  Oregon,  Nevada,  and  California. 


I76 


A  Study  of  the  Sky. 


Time  distri- 
bution in 
Great  Britain. 


Watches. 


The  Breguet 
spring. 


Compensation 
for  temperature. 


One  of  the  most  elaborate  systems  of  time  distribution 
is  to  be  found  in  Great  Britain.  The  Royal  Observatory 
at  Greenwich  is  the  source  of  accurate  time,  which  is 
telegraphed  over  the  United  Kingdom.  A  time  ball  is 
dropped  at  Greenwich,  for  the  use  of  ships  in  the 
Thames.  Another  at  Deal  serves  the  shipping  in  the 
Downs.  The  great  clock  at  Westminster  Palace  is 
regulated  in  accordance  with  the  telegraphic  signals. 
Through  the  post-office  department  are  sent  signals 
which  are  utilized  in  various  ways,  such  as  the  regulation 
of  clocks,  the  striking  of  bells,  and  the  firing  of  guns. 

However  elaborately  accurate  time  may  be  distributed 
in  a  given  city,  business  men  rely  upon  their  watches, 
which  are  compared  from  time  to  time  with  some  time- 
piece supposed  to  be  a  standard.  The  price  of  a  watch 
movement  is,  in  general,  a  good  indication  of  its  quality  ; 
so  excellent  are  the  products  of  American  makers,  that 
one  need  not  buy  a  foreign  watch  in  order  to  get  a  good 
timepiece.  In  purchasing  a  watch  of  moderate  price 
one  may  get  an  approximate  idea  of  its  excellence  by 
paying  attention  to  certain  details.  The  more  jewels 
the  better.  The  hair-spring  should  be  composed  of  a 
number  of  closely  packed  coils  ;  if  the  end  of  the  outer- 
most coil  comes  in  toward  the  center,  overlying  the 
other  coils,  the  hair-spring  is  a  "  Breguet,"  which  is  the 
best  form.  The  rim  of  the  balance  wheel  should  be 
made  of  two  metals,  the  outer  one  brass  and  the  inner 
one  steel.  This  combination  is  of  no  use  unless  the  rim 
has  been  cut  through  at  two  opposite  points. 

A  fair  compensation  for  changes  of  temperature  is 
obtained  by  using  this  form  of  balance.  All  modern 
American  movements,  unless  very  cheap,  have  compen- 
sation balances.  When  hot  weather  comes  the  hair- 
spring loses  strength,  and  the  balance  must  become 


Time. 


177 


smaller  in  diameter,  if  it  is  to  be  driven  as  rapidly  as 
before.  The  brass  in  the  rim  expands  in  the  heat  more 
than  the  steel  does  ;  thus  each  half  of  the  rim  is  bent 
inward,  and  the  diameter  of  the  balance  grows  less. 
When  the  watch  is  exposed  to  cold  the  hair-spring 
acquires  more  vigor,  and  the  watch  tends  to  gain  ;  but 
the  outer  brass  portion  of  the  rim  contracts  more  than 
the  inner  steel  portion,  and  each  half  of  the  ring  bends 
outward,  increasing  the  inertia  of  the  wheel,  and  thus 
preventing  the  gain  which  would  otherwise  ensue. 

To  test  the  running  of  a  watch  one  should  compare  it  The  rate  of 
with  a  standard  clock 
every  day,  or  even 
more  often,  until  a 
satisfactory  knowl- 
edge of  its  perform- 
ance has  been  ob- 
tained. A  watch 
which  is  set  right  to- 
day and  found  nearly 
correct  a  month  after- 
ward may  meanwhile 
have  wandered  off 

two  or  three  minutes,  FIG.  90.— A  WATCH  BALANCE. 

and  come  back  again.  Sometimes  a  watch  exhibits  a 
large  daily  variation,  gaining  a  considerable  fraction  of  a 
minute  during  the  first  few  hours  after  it  is  wound,  and 
losing  it  during  the  remainder  of  the  day. 

It  is  needless  to  say  that  a  watch  must  be  treated  well, 
if  it  is  expected  to  do  good  work.  It  must  not  be 
handled  carelessly,  nor  be  permitted  to  run  down  ;  if  it 
runs  down,  it  rarely  starts  again  with  the  same  rate  that 
it  had  previously.  Unless  a  watch  is  expensive,  and 
' '  adjusted  for  heat,  cold,  and  position, "  it  is  likely  to 


Good  treat- 
ment. 


I78 


A  Study  of  the  Sky. 


Ladies  cul- 
pable. 


The  regulator. 


Miscellaneous 
facts. 


exhibit  considerable  variations  of  rate,  if  it  is  not  kept  in 
nearly  the  same  position  at  night  as  in  the  daytime.  It 
is  not  a  good  plan  to  put  a  watch  under  one's  pillow. 

Ladies  are  especially  culpable  in  the  matter  of  hand- 
ling their  watches.  They  do  not  wind  them  regularly, 
and  they  let  them  lie  around  in  bureau  drawers  or 
handkerchief  boxes,  or  other  places  where  they  are  con- 
sidered safe  for  the  time  being.  For  these  reasons 
ladies'  watches  rarely  keep  good  time. 

A  young  man  is  likely  to  move  the  regulator  too 
often.  If  his  watch  suddenly  begins  to  gain  a  few 
seconds  a  day,  the  regulator  is  moved  backward  at 
once.  The  less  one  alters  the  regulator  the  better,  for 
a  watch,  like  a  human  being,  is  subject  to  spells  of 
irregularity,  from  which  it  recovers  if  left  to  itself. 

If  the  minute-hand  is  once  set  exactly  over  a  minute 
mark,  when  the  second-hand  is  at  60,  and  the  two 
hands  do  not  keep  together,  either  the  face  is  poorly 
engraved,  or  the  pinion  on  which  the  minute-hand  turns 
is  not  in  the  center  of  the  face.  If  either  of  these  hands 
slipped,  which  is  rarely  the  case,  the  same  effect  would 
be  produced. 

Occasionally  a  watch  gains  a  minute  or  so  in  an  hour; 
this  indicates  that  the  hair-spring  is  caught,  so  that  it 
does  not  vibrate  freely  ;  a  jeweler  will  loosen  it  in  a 
moment.  A  watch  may  stop  because  it  has  been 
wound  too  tightly  ;  a  little  shaking  for  a  few  minutes  in 
such  a  way  as  to  make  the  balance  wheel  vibrate  will 
relieve  the  difficulty. 

In  general,  the  possessor  of  a  watch  does  his  full  duty 
by  it  if  he  winds  it  regularly,  handles  it  carefully,  keeps 
it  in  the  same  position  as  much  as  possible,  and  has  it 
cleaned  once  in  two  years. 


CHAPTER   XL 

THE    SUN. 

"  See  the  sun  ! 
God's  crest  upon  His  azure  shield  the  heavens." 

— Bailey. 

OF  all  the  heavenly  bodies  the  sun  is  of  the  greatest 
importance  to  man.  Without  its  steady  gravitational  its  importance, 
pull  on  the  earth  our  planet  would  fly  away  to  unknown 
regions  of  space,  and  the  chill  of  death  would  settle 
down  upon  it.  The  oceans  would  stiffen  into  glass  : 
the  rivers  would  halt  in  their  courses.  All  the  higher 
forms  of  vegetable  life  would  wither  and  die,  and 
humanity,  having  struggled  in  vain  against  inevitable 
fate,  would  perish  of  hunger  and  cold.  For  the  human 
race  is  dependent  upon  the  energy  which  the  sun 
radiates  so  lavishly. 

The  sun  stimulates  the  growing  plant  to  disengage 
carbon  from  the  embrace  of  oxygen,  feeding  on  the 
carbon  and  leaving  the  oxygen,  which  is  necessary  for 
the  life  of  men  and  animals.  Its  heat  evaporates  the 
waters  of  the  oceans,  which  rise,  form  clouds,  and 
descend  again  as  rain  or  dew,  quenching  the  longings 
of  the  parched  earth,  nourishing  vegetation,  coursing  in 
majestic  rivers  to  the  sea,  refreshing  the  bodies  of  men 
and  animals,  and  giving  delight  to  all  intelligent  spirits. 

The  energies  of  the  sunbeams  were  stored  ages  ago  in 
primeval  forests  :  the  forests  were  overwhelmed  by  the 
mighty  deep  and  buried  in  a  sepulcher  of  stone.  To- 
day men  dig  up  the  mummified  sunbeams  and  burn 

179 


i8o 


A  Study  of  the  Sky. 


Mummified 
sunbeams. 


The  staff  of 
life. 


them  in  their  furnaces  and  fireplaces.  The  genial  light 
of  the  grate  fire  is  due  to  those  ancient  sunbeams  which 
are  now  released  from  their  prison  house.  The  flying 
locomotive,  beneath  whose  impetuous  rush  the  earth 
trembles,  gets  its  speed  from  the  sunbeams.  The  white- 
hot  glow  of  a  Bessemer  converter  comes  primarily  from 
the  sun.  The  water  which  flows  into  our  houses  has 
been  purified  by  the  sun's  rays,  and  has  been  forced 
through  the  pipes  by  great  engines  which  derive  their 
power  from  solar  energy  stored  in  coal.  The  electric 
car  is  driven  by  a  current  generated  by  a  dynamo,  and 
the  dynamo  in  turn  by  a  steam  engine  which  is  fed 
with  the  sunbeams  of  bygone  ages.  The  electric  light, 
which  turns  night  into  day,  is  stray  sunshine.  Nearly 
all  the  heavy  work  of  the  civilized  world  is  done  by  the 
sun. 

Bread,  which  is  the  staff  of  life,  comes  from  wheat 
which  has  been  stimulated  in  its  growth  by  the  sun- 
beams, and  moistened  by  water  lifted  by  the  sun.  If 
the  mill  which  reduced  the  wheat  to  flour  was  driven  by 
the  wind,  we  find  the  source  of  the  wind  in  heat  pro- 
duced by  the  sun's  rays.  If  the  mill  was  driven  by 
water  power  or  by  steam,  we  still  say  that  the  sun  sup- 
plied the  power  which  turns  the  millstones.  Even  the 
final  process  of  baking  the  bread  is  an  application  of 
heat  originally  derived  from  the  sun.  A  man's  muscles 
obtain  their  strength  from  the  food  which  he  has  eaten  : 
in  the  food  has  been  stored  the  energy  of  the  sun. 

In  fine,  we  owe  to  the  sun  the  sustenance  of  our 
bodies,  the  maintenance  of  our  physical  energies,  the 
comforts  which  we  enjoy,  the  cooling  breeze,  the  gentle 
shower,  and  the  manifold  beauties  of  nature.  We  pro- 
ceed therefore  to  a  short  study  of  this  wonder-working 
body,  and  shall  endeavor  to  gain  some  notions  about  its 


The  Sun.  181 


distance,  its  size,  its  motion,  its  changes  of  appearance, 
its  make-up,  its  energies,  and  its  future. 

The  distance  of  the  sun  from  the  earth  is  nearly  The  sun's 
93,000,000  miles.  If  a  straight  road  were  built  from  c 
the  earth  to  the  sun,  and  the  earth,  rotating  at  its 
present  speed,  were  to  start  along  this  highway,  like  a 
rolling  wheel,  more  than  ten  years  would  elapse  before 
it  would  reach  the  sun.  For  in  one  day  it  would  travel 
a  distance  equal  to  its  own  girth,  which  we  will  call 
25,000  miles.  In  forty  days  1,000,000  miles  would 
have  been  left  behind  ;  over  3,700  days  would  therefore 
be  consumed  in  the  entire  journey.  An  express  train* 
traveling  fifty  miles  an  hour  day  and  night,  without 
intermission,  would  require  over  two  centuries  to  trav- 
erse the  same  distance. 

There  are  many  ways  of  finding  the  distance  of  the  Howthedis 
sun,  most  of  which  involve  complicated  mathematical  tance  is  found, 
operations.  But  one  of  them  is  easily  understood.  By 
a  series  of  beautiful  and  accurate  experiments  physicists 
have  measured  the  velocity  of  light,  which  they  place  at 
186,330  miles  a  second.  Astronomers  have  found  that 
light  takes  499  seconds  to  come  from  the  sun.  There- 
fore the  distance  of  the  sun  is  obtained  by  multiplying 
these  two  numbers  together.  This  is  the  mean  distance 
of  the  earth  from  the  sun.  Since  the  orbit  of  the  earth 
is  not  a  perfect  circle,  but  an  ellipse,  its  distance  from 
the  sun  varies.  It  is  nearest  to  the  sun  at  the  beginning 
of  the  year;  six  months  later,  on  July  i,  it  is  almost 
3,000,000  miles  further  away. 

When  the  distance  of  the  sun  is  known  its  diameter 
is  easily  computed.      It  is  866,500  miles;  this  is  nearly   The  diameter, 
no  times  the  earth's  diameter.     The  sun  is  therefore 
over  1,300,000  times  as  large  as  the  earth.      If  the  earth 
were  magnified  until  it  became  as  large  as  the  sun,  and 


182 


A  Study  of  the  Sky. 


Use  of  a 
telescope. 


Spots. 


Rotation. 


the  sizes  of  its  inhabitants  were  increased  in  like  ratio,  a 
man  originally  5  feet  1 1  inches  in  height  would  become 
650  feet  tall.  If  the  force  of  gravity  were  no  stronger 
than  at  present,  his  original  weight  would  be  multiplied 
by  1,331,000.  But,  according  to  the  principles  of 
mechanics,  the  earth's  attraction  for  a  body  upon  its 
surface  would  be  no  times  as  great  as  before  ;  hence 
our  unfortunate  human  being  would  weigh  over  10,000,- 
ooo  tons,  if  his  former  weight  was  only  140  pounds. 

When  the  sun  is  viewed  with  a  telescope  especial  pre- 
cautions are  taken  to  diminish  the  intense  light,  so  that 
the  eye  of  the  observer  may  not  be  ruined.  A  very 
dark  glass  held  in  front  of  the  eye  will  furnish  the  needed 
protection,  but  it  may  become  too  hot  and  break.  Special 
forms  of  eyepieces  have  been  devised,  which  allow  most 
of  the  light  and  heat  to  escape,  reflecting  only  a  small 
part  of  it  to  the  observer's  eye. 

A  cursory  examination  with  even  a  small  telescope 
reveals  the  existence  of  small  black  spots  upon  the  solar 
surface.  Each  spot  is  surrounded  by  a  lighter  border, 
which  appears  to  be  composed  of  a  large  number  of  fila- 
ments, like  the  fringe  around  a  table-mat.  The  dark 
portion  of  the  spot  is  called  its  umbra  ;  the  surrounding 
border  is  the  penumbra. 

If  an  observer  makes  a  drawing  showing  the  posi- 
tions of  the  spots  on  the  solar  disc,  and  looks  at  them 
again  in  a  day  or  two,  he  sees  that  they  have  moved.  A 
watch  of  a  few  days  will  convince  him  that  they  are 
being  carried  around  at  a  pretty  regular  rate,  and  that 
the  sun,  like  the  earth,  turns  on  an  axis,  making  a  com- 
plete rotation  in  three  weeks  and  a  half. 

Spots  near  the  solar  equator  revolve  in  twenty-five 
days  and  a  fraction  ;  those  which  are  nearly  midway 
between  the  poles  and  the  equator  consume  twenty- 


The  Sun. 


183 


seven  days  in  making  one  revolution.     Spots  are  never 

seen  more  than  half  way  from  the  equator  to  the  poles,    JJistri bution  of 

and  are  much  less  numerous  near  the  equator  than  a  few 

degrees  away  from  it.     This  strange  distribution  of  the 

spots,   together  with  the  curious  irregularity   in    their 


\ 


FIG.  91.— SUN-SPOTS. 

times  of  revolution,  constitutes  the  first  of  a  number  of 
unexplained  mysteries  concerning  the  solar  surface. 

When  a  large  spot  is  on  the  edge  of  the  sun's  disc, 
one  may  see  that  it  makes  a  slight  notch  in  the  sun's  depression, 
limb  (as  the  edge  of  the  disc  is  called).  Therefore 
the  spot  must  be  a  depression  below  the  grayish-white 
surface  of  the  sun.  The  shape  of  the  spot  is  like  that  of 
a  dinner  plate,  the  bottom  of  the  plate  corresponding  to 


1 84 


A  Study  of  the  Sky. 


Sizes  of  spots. 


the  umbra,  and  the  gently  sloping  rim  to  the  penumbra. 

Spots  vary  in  size  from  the  merest  black  points,  just 

visible  with  high  telescopic  power,  to  immense  objects, 


r 


12 


A  large  spot- 
group. 


FIG.  92.— CHANGES  IN  A  SOLAR  SPOT. 

covering  thousands  of  millions  of  square  miles.  One  of 
the  largest  spot-groups  on  record  had  a  diameter  of 
150,000  miles.  The  central  spot  of  a  large  group, 


•The  Sun.  185 


which  appeared  in  February,  1892,  measured  100,000 
miles  by  50,000  miles.  Such  enormous  objects  are 
easily  visible  to  the  naked  eye  if  it  be  protected  by  a 
dark  glass. 

Sun-spots  change  their  appearance  from  day  to  day, 
and  frequently  from  hour  to  hour.  At  times  a  white  Their  changes, 
bridge  may  span  the  black  gulf  of  the  umbra  ;  at  other 
times  the  umbra  may  be  almost  entirely  hidden  by  a 
grayish  veil  similar  in  appearance  to  terrestrial  clouds. 
The  filaments  of  the  penumbra,  which  are  usually  nearly 
straight,  may  become  violently  curved  and  distorted. 
Occasionally  the  appearance  of  the  filaments  indicates 
that  the  spot  has  a  rotary  motion,  like  that  of  a  terres- 
trial whirlwind.  A  spot  frequently  breaks  up  into  a  mul- 
titude of  smaller  ones.  A  group  of  small  ones  may 
coalesce  into  a  single  large  one. 

In  July,    1892,  a  double  sun-spot,   consisting  of  two 

i  i_    •    i       i_    -j  J  jj     A  solar  tempest. 

umbrae,  separated  by  a  bright  bridge,  and  surrounded 
by  a  common  penumbra,  experienced  a  very  rapid 
change  of  appearance.  A  bright  jet  of  white  matter 
shot  out  over  one  of  the  umbrae,  and  when  photographed 
presented  the  appearance  of  a  gigantic  fish-hook,  carry- 
ing at  its  extremity  a  huge  ball  of  light.  This  was 
but  the  precursor  of  a  terrific  commotion,  for,  after  half 
an  hour,  it  was  found  that  a  multitude  of  outbursts  had 
taken  place,  so  that  the  spot  was  completely  hidden. 
This  solar  storm,  which  extended  over  billions  of  square 
miles,  was  not  in  the  sun-spot,  but  high  above  it.  Some- 
times, when  our  atmospheric  conditions  are  peculiar,  a 
clear  sky  is  converted  into  a  cloudy  one  in  the  course  of 
a  few  minutes,  and  the  clouds  pass  away  again  in  a  few 
hours.  The  solar  disturbance  behaved  in  a  similar 
fashion  ;  in  two  hours  after  the  disappearance  of  the 
spot  it  was  again  in  view,  unscathed  by  the  tempest. 


1 86 


A  Study  of  the  Sky. 


Duration  and 
death. 


Periodicity. 


The  photo- 
sphere. 


A  sun-spot  usually  lasts  a  few  weeks  ;  one  is  on 
record  which  was  observed  for  eighteen  months.  The 
death  of  a  sun-spot  is  a  short  process.  The  surround- 
ing material  rushes  pell-mell  into  the  cavity,  and  all  is 
over. 

One  of  the  most  remarkable  facts  about  sun-spots  is 
their  periodicity.  At  times  the  sun  is  almost  free  from 
them  for  a  number  of  successive  weeks.  At  other  times 
they  are  to  be  counted  by  tens  and  even  run  up  into  the 
hundreds.  When  the  first  quarter  of  the  nineteenth 
century  had  been  rounded  out,  a  persevering  German, 
Schwabe  by  name,  who  was  a  magistrate  in  the  town  of 
Dessau,  being  possessed  of  a  telescope  and  a  large  fund 
of  patience,  resolved  that  he  would  watch  the  sun  day 
by  day  and  count  the  number  of  spots.  So  it  came  to 
pass  that  the  sun  found  Schwabe  continually  on  the  alert 
for  over  forty  years. 

An  examination  of  his  record  books,  after  he  had 
been  at  work  nearly  twenty  years,  revealed  something 
quite  unexpected.  He  quaintly  said  that,  like  Saul,  he 
went  out  to  seek  his  father's  asses,  and  found  a  king- 
dom. His  discovery  was  that  there  was  a  certain 
regularity  about  the  number  of  spots  visible.  If  spots 
were  decidedly  scarce  in  a  given  year,  the  next  year  the 
number  was  larger,  the  next  year  larger  still,  and  so  on, 
until  the  fifth  or  sixth  year,  when  the  number  was 
greatest ;  during  the  ensuing  year  they  were  fewer,  and 
after  that  their  number  diminished  until  it  became  a 
minimum  again.  Eleven  years  and  a  fraction  elapse 
between  one  minimum  and  the  next  one.  The  period 
of  eleven  years  is  subject  to  irregular  variations  of  a  year 
or  more. 

Considerable  light  is  thrown  on  the  nature  of  sun- 
spots  by  a  knowledge  of  the  medium  in  which  they 


The  Sun. 


187 


reside.  It  is  called  the  photosphere,  because  it  is  the 
light-giving  surface  directly  visible  to  us.  It  is  analo- 
gous to  the  crust  of  the  earth,  but  is  far  from  being 
solid.  The  heat  of  the  sun  is  so  intense  that  any  known 
solid  would  be  quickly  melted  and  vaporized,  if  dropped 


Photosphere 
not  solid. 


FIG.  93. — A  PORTION  OF  THE  PHOTOSPHERE. 

into  its  fiery  bosom.  The  photosphere  is  a  sheet  of 
luminous  clouds,  floating  in  an  intensely  heated  gas,  as 
terrestrial  clouds  float  in  our  atmosphere.  It  is  not  of 
uniform  brightness,  but  consists  of  a  grayish  back- 
ground, plentifully  besprinkled  with  comparatively  small 
masses  of  greater  brightness.  If  great  things  may  be 
compared  with  insignificant  ones,  the  photosphere  may 


1 88  A  Study  of  the  Sky. 

be  said  to  resemble  a  plate  of  rice-soup.  The  solar 
' '  rice-grains ' '  average  500  miles  in  width,  and  are 
themselves  composed  of  smaller  "granules,"  compacted 
together. 

Three  quarters  of  the  sun's  light  is  derived  from  the 
rice-grains,  which  cover  about  one  fifth  of  the  entire 
surface.  They  are  by  some  supposed  to  be  the  upper 
ends  of  ascending  currents,  rising  from  the  intensely 
heated  interior  ;  the  dark  spaces  between  the  spots, 
according  to  this  view,  mark  the  terminations  of  streams 
of  matter  which  have  been  cooled  somewhat  and  are 
descending.  The  penumbrae  of  sun-spots  contain  long- 
drawn-out  rice-grains. 

The  solar  The   interior   of   the   sun   is   thought   to   be   mainly 

gaseous,  because  of  the  intense  heat  which  must  prevail 
there.  Near  the  center  the  gases  may  be  changed  to 
liquids  because  of  the  enormous  pressure  of  the  superin- 
cumbent fluids.  A  heat,  the  intensity  of  which  no  man 
has  the  temerity  to  estimate,  strives  to  expand  the  gases 
imprisoned  beneath  the  overlying  photosphere. 

From  time  to  time  outbursts  occur  at  weak  places  in 
the  photosphere ;  the  pressure  from  below  is  temporarily 
relieved  in  the  locality  of  the  outbreak,  and  the  photo- 
sphere in  that  region  sinks  a  little,  forming  the  shallow 
basin  of  a  sun-spot.  The  uprushing  gaseous  matter,  like 
a  stream  of  water  thrown  by  a  fire  engine,  rises  to  a 
certain  height,  and  falls  back  again  upon  the  solar 
surface. 

origin  of  a  spot.  But  w^y  *s  the  umbra  of  a  sPot  so  dark?  Since  the 
umbra  is  depressed  below  the  general  level,  and  is  over- 
laid by  a  greater  depth  of  cooler  vapors  than  the 
adjacent  regions,  it  looks  darker  than  they.  For  the 
light  from  the  umbra,  coming  up  through  the  vapors, 
is  partially  absorbed  ;  the  umbra  therefore  looks  dark 


The  Sun. 


in  contrast  with  the  surrounding  portions  of  the  photo- 
sphere.     However,    the    darkest    portion   of   a   spot    is   Acalcium 
brighter  than  a  calcium  light.     When  the  force  of  the  Hsht- 
eruption  has  expended  itself  and  hot  gases  are  no  longer 
thrown  up  to  great  heights,   to  be  cooled  and  precip- 
itated upon  the  solar  surface,  the  spot  ceases  to  exist. 

Such,  in  brief  outline,  is  the  most  reasonable  theory 
concerning  the  nature  of  sun-spots.  Many  other 
theories  have  been  put  forth  from  time  to  time,  but  they 
all  seem  open  to  very  serious,  if  not  fatal,  objections. 

No  satisfactory  explanation  has  yet  been  advanced  for 
the  periodicity  of  spots,  or  for  their  absence  from  the 
polar  regions.  The  paucity  of  our  knowledge  concern- 
ing these  solar  storms  is  not  astonishing,  in  view  of  our 
ignorance  about  the  whirlwinds  and  cyclones  which  stir 
up  limited  portions  of  our  own  atmosphere. 

While  the  photosphere  is  depressed  in  the  locality 
where  a  sun-spot  lies,  it  is  elevated  in  numerous  other 
places.  The  elevations  are  called  facula,  and  are  Facui<z. 
specially  numerous  in  the  neighborhood  of  spots.  The 
agitations  to  which  the  photosphere  is  subject  seem  to 
raise  its  outer  surface  in  mountainous  ridges  and  isolated 
crests  like  the  waves  of  a  choppy  sea.  These  elevations 
of  photospheric  matter  sometimes  rise  to  a  height  of 
several  hundred  miles,  and  look  much  brighter  than  the 
surrounding  regions,  as  there  is  less  gas  above  their 
summits  to  absorb  their  light  on  its  journey  to  our  eyes. 
Recent  photographs  show  that  the  fainter  faculce  extend 
in  a  network  over  the  entire  photosphere,  as  shown  in 
Fig.  94.  The  sensitive  plates  bear  mute  witness  to  the 
photospheric  tumults. 

When  the  moon  causes  a  total  eclipse  of  the  sun  by  The  chromo- 
coming  between  that  luminary  and  the  earth,  it  covers  sphere> 
up  the  dazzling  photosphere,  and  permits  less  brilliant 


A  Study  of  the  Sky. 


A  scarlet 
envelope. 


Prominences. 


gases  in  its  vicinity  to  be  seen.  The  photosphere  is 
thus  found  to  be  covered  by  a  scarlet  envelope  called 
the  chromosphere  (color  sphere).  Its  depth  is  5,000 


FIG.  94.— FACUL^E. 

miles,  and  it,  like  the  photosphere,  is  agitated  by  tremen- 
dous forces. 

Rising  from  it  are  beautiful  scarlet  forms  of  various 
shapes,  which  have  been  named  protuberances,  or 
prominences.  Some  of  them  look  like  huge  trees,  with 
trunks  thousands  of  miles  in  diameter,  and  tops  spread- 
ing out  to  great  distances.  The  top  of  such  a  promi- 
nence is  often  connected  with  the  chromosphere  by 


The  Sun. 


191 


smaller  trunks,  so  that  the  whole  resembles  a  huge 
banyan  tree.  Some  look  like  jets  of  fiery  liquid,  and  Fieryjets. 
remind  one  of  the  streams  of  water  thrown  by  fire 
engines.  A  few  resemble  huge  billows  of  flame.  Some- 
times cloud-like  masses  of  chromospheric  matter  float 
above  the  chromosphere,  having  no  apparent  connection 
with  it.  One  has  been  noticed  which  was  475,000 
miles  above  the  solar  surface.  Thanks  to  the  spectro- 
scope these  beautiful  objects  may  now  be  observed  any 
clear  day  when  the  sun  is  shining  in  its  full  strength. 
The  most  interesting  prominence  ever  seen  was  ob- 


FIG.  95.— PROMINENCES. 


served  in  the  fall  of  1871  by  Prof.   Chas.   A.  Young.*   A  remarkable 
One  day  at  noon  he  was  looking  at  one  of  these  objects,   * 
which  was  a  long,  low,  red  cloud,  connected  by  four  or 
five  stems  with  the  chromosphere.     It  was  remarkable 


*  Director  of  the  observatory  at  Princeton,  N.  J. 


A  Study  of  the  Sky. 


A.n  explosion. 


Two  classes  of 
prominences. 


only  for  its  size,  being  about  100,000  miles  long  and 
half  as  broad.  At  12:30  p.  m.  he  was  called  away, 
having  noticed  nothing  special,  except  that  below  one 
end  of  the  prominence  a  small  bright  lump  had  de- 
veloped on  the  solar  surface.  In  twenty-five  minutes 
he  returned,  but  the  prominence  was  gone.  The  small 
bright  lump  had  apparently  become  a  surging  flame, 
rising  to  a  height  of  50,000  miles.  The  prominence 
had  been  blown  into  shreds  by  some  tremendous  ex- 
plosion, and  the  d6bris  of  its  wreck  was  rising  400 


FIG.  96.— A  QUIESCENT  PROMINENCE. 

times  as  swiftly  as  a  rifle  bullet  flies.  In  ten  minutes  it 
had  reached  a  height  of  200,000  miles.  At  1:15  p.  m. 
only  a  few  shreds  of  the  prominence  were  visible. 

Prominences  are  divided  into  two  classes,  the  quiescent 
and  the  eruptive.  The  former  are  the  cloud-like  forms 
which  have  been  already  mentioned  ;  they  are  com- 
posed mainly  of  hydrogen  and  helium.*  The  latter  are 
fiery  fountains  which  sometimes  rush  forth  with  veloci- 

*  When  helium  was  named  it  was  supposed  to  be  found  in  the  sun  alone. 
But  it  was  discovered  along  with  argon,  and  has  since  been  found  in  rare 
minerals.  It  also  rises  from  particular  springs  in  the  Black  Forest  and  else- 
where. 


The  Sun.  193 


ties  exceeding  300  miles  a  second.  •  Since  the  velocity  is 
never  measured  at  the  start,  when  it  is  greatest,  before 
it  has  been  diminished  by  the  resistance  of  the  gas 
through  which  it  flies,  and  by  the  backward  pull  of  the 
sun,  which  is  nearly  twenty-eight  times  as  great  as  the 
pull  at  the  earth's  surface,  its  original  value  may  be  as 
great  as  500  miles  a  second.  Some  of  these  eruptions 
hurl  masses  of  heated  gas  so  swiftly  that  the  sun's 
attraction  cannot  hold  them  back,  and  they  escape  into 
space,  are  condensed  into  solid  bodies,  and  fly  away  to 
regions  unknown. 

The  lightning-girt  cyclone  strikes  terror  to  men's  Thefuryof 
hearts,  as  it  plows  through  a  town,  uprooting  the  stur- 
diest  trees,  and  tearing  in  pieces  structures  of  solid 
masonry.  But  how  insignificant  it  is  compared  with  a 
jet  of  glowing  gas,  which  travels  further  in  a  second 
than  the  cyclone  does  in  an  hour,  and  which,  if  it  should 
strike  the  continent  of  North  America,  would  turn  its 
surface  into  a  glowing  cinder  in  a  minute. 

Such  a  storm,  "  coming  down  upon  us  from  the  north, 
would  in  thirty  seconds  after  it  had  crossed  the  St. 
Lawrence  be  in  the  Gulf  of  Mexico,  carrying  with  it 
the  whole  surface  of  the  continent  in  a  mass,  not  simply 
of  ruin,  but  of  glowing  vapor,  in  which  the  vapors 
arising  from  the  dissolution  of  the  materials  composing 
the  cities  of  Boston,  New  York,  and  Chicago  would  be 
mixed  in  a  single  indistinguishable  cloud."  A  terrestrial 
volcano  may  bury  a  city  and  cause  the  waters  of  an 
adjacent  sea  to  boil.  But  many  a  solar  eruption  could 
fuse  the  earth  into  a  misshapen  lump. 

What  is  found  beyond  the  chromosphere  ?     At  the 

,  ,.          .  ,    ,  The  corona. 

instant  when  a  solar  eclipse  becomes  total,  and  the  moon 
hangs  in  mid-heaven,  a  black  ball,  fringed  with  the  rosy 
prominences,  it  is  surrounded  by  sheets  of  soft,  pearly 


The  Sun.  195 


light,  which  form  an  aureole  of  surpassing  beauty. 
The  aureole  has  received  the  name  ' '  corona, "  as  it  is  a 
crown  of  light  upon  the  king  of  day.  Its  form  varies. 
At  times  it  is  small  in  extent  and  roughly  quadrangular 
in  form.  At  other  times  it  extends  out  in  great  stream- 
ers, as  if  the  sun  had  wings.  Streamers  nearly  9,000,- 
ooo  miles  in  length  were  observed  in  1878  from  the  sum- 
mit of  Pike's  Peak.  Close  to  the  sun  the  corona  is 
bright,  in  marked  contrast  with  the  filmv  streamers  ; 
the  inner  corona  is  composed  of  fine  filaments,  closely 
packed  together,  which  a  small  telescope  shows  beauti- 
fully. They  closely  resemble  the  finest  of  human  hair. 

The  corona  is  not  to  be  considered  as  a  solar  atmos-   Not  a  soiar 
phere.      Were  that  atmosphere, 

the  case,  it  would 
decrease  in  density 
with  a  certain  reg- 
ularity the  further 
it  extended  from  the 
sun  ;  it  would  also 
extend  to  about  the 
same  distance  on  all 
sides  of  the  sun. 

When    examined 
with  the    spectro-       FlG-  9s-— THE  CORONA  OF  JANUARY,  1889. 
scope  it  yields  two  different  spectra.     There  is  a  faint  The  s  ectra 
continuous  spectrum,  which  may  come  from  sunlight  re- 
flected from  the  materials  composing  the  corona,  or  may 
be  caused  directly  by  white-hot  solid  or  liquid  particles 
scattered  through  the  corona.     The  other  spectrum  is  a 
bright-line  spectrum  coming  from  a  glowing  gas.     The 
most  prominent  line  in  it  is  not  identical  with  the  spec- 
tral line  of  any  substance  found  on  the  earth  ;  the  name 
"coronium"  has  been  proposed  for  the  unknown  sub- 


A  Study  of  the  Sky. 


Filaments. 


stance  which  causes  it.      Other  lines  reveal  the  presence 
of  hydrogen  and  helium. 

Whence  are  these  curious  interlacing  filaments  of  the 
inner  corona,  and  the  outstretched  wings  of  the  outer 


FIG.  99.— THE  CORONA  OF  APRIL,  1893. 


corona 


Dark  rifts. 


Why  are  dark  rifts  seen  in  certain  places,  as  if 
the  corona  had  been  cleft  by  a  gigantic  cleaver  from  its 
outermost  boundaries  straight  down  to  the  solar  surface? 
How  are  the  materials  composing  the  corona  upheld 


The  Sun.  197 


against  the  gravitational  pull  of  the  sun  ?  To  these  and 
other  similar  queries  astronomers  reply  frankly  that 
their  knowledge  is  inadequate. 

That  the  coronal  matter  is  excessively  rarefied  in  its   Rarefied 
higher  regions  is  proven  by  the  fact  that  several  comets  matter. 
have  passed  through  it  without  any  perceptible  change 
in  their  motion.     This  rarefied  matter  may  be  upheld 
by  an  electrical  repulsion  originating  in  the  sun. 

The  fine  filaments  are  due,  perchance,  to  streams  of  Causeofthe 
gas,  which  the  sun  is  continually  ejecting.    Their  curved  filaments, 
forms  and  apparent  interlacings  are  thought  by  Professor 
Schseberle*  to  be  due  to  the  sun's  rotation. 

Let  us  recapitulate  what  has  been  stated  concerning 
the  make-up  of  the  sun: 

I.  The  interior  of  the  sun  is  supposed  to  be  mainly  The  sun's 
gaseous,  the  expansive  power  of  the  gases  being  held  in  make-uP- 
check  by  the  grip  of  gravitation. 

II.  As  the  film  of    a   soap-bubble   confines   the  air 
within  it,  so  the  photosphere,  which  is  the  home  of  the 
sun-spots,  strives  to  confine  the  imprisoned  gases.     It  is 
composed  of   vapors  which  have  been  somewhat  con- 
densed by  their  proximity  to  the  cold  of  outer  space. 

III.  Certain  light  gases  which  do  not  condense   so 
readily  as  those  of  which  the  photosphere  is  composed 
form  a  shallow  layer  covering  the  photosphere.     The 
layer  is  of  a  scarlet  hue,  nourishes  the  prominences,  and 
is  called  the  chromosphere. 

IV.  Beyond  the  chromosphere,  and  to  a  certain  extent 
mingled  with  it,  is  the  pearly  corona,  whose  mysterious 
filaments  and  vast  extension  furnish  food  for  much  spec- 
ulation. 

Bright  as  full  sunshine  is,  it'  may  be  compared  with  An  experiment 
the  light  of  a  candle.     Light  screens  are  placed  over  with  sunlisht- 

*  J.  M.  Schaeberle,  of  the  Lick  Observatory. 


198 


A  Study  of  the  Sky. 


A  standard 
candle. 


the  windows  of  a  room  so  that  it  is  completely  darkened. 
A  small  hole  is  made  in  one  screen  and  a  lens  inserted 
in  it.  By  manipulating  a  mirror  outside,  a  horizontal 
beam  of  sunlight  is  thrown  through  the  lens,  which 
spreads  out  the  beam  of  light,  so  that  it  illuminates  a 
large  circle  on  the  opposite  wall.  If  the  diameter  of  the 
circle  is  200  times  the  diameter  of  the  lens,  the  area  of 
the  circle  is  200  x  200,  or  40,000  times  as  great  as  that 
of  the  lens.  Therefore  the  beam  of  sunlight,  when  thus 
spread  out,  has  only  OT&inr  of  its  former  intensity.  A 
pencil  is  held  in  the  enfeebled  sunlight,  close  to  the 
wall,  so  that  its  shadow  is  cast  there. 

A  standard  candle  is  lighted  and  held  in  such  a  direc- 
tion from  the  pencil  that  the  shadow  which  it  casts  on 
the  wall  is  near  the  shadow  cast  by  the  sunlight.  The 
candle  is  placed  at  such  a  distance  from  the  pencil  that 
the  two  shadows  appear  of  equal  intensity.  In  this 
manner  the  enfeebled  sunlight  is  compared  with  the 
light  of  a  standard  candle. 

The  intensity  of  the  light  of  the  full  moon  may  be 
estimated  in  the  same  way  ;  it  is  found  that  sunlight  is 
600,000  times  as  bright  as  the  light  of  the  full  moon. 
An  arc  light  approaches  sunlight  in  intensity  more 
nearly  than  any  other  artificial  light.  Yet  if  we  view 
with  a  dark  glass  an  arc  light  which  is  directly  in  line 
with  the  sun,  it  appears  as  a  dark  spot  on  the  solar  sur- 
face. It  is  about  one  third  as  intense  as  sunlight. 

The  amount  of  heat  which  the  sun  sends  to  the  earth 
The  sun's  heat.  jg  determined  by  allowing  a  beam  of  sunlight  to  shine 
upon  a  quantity  of  water,  and  measuring  the  rise  of 
temperature  thus  caused.  In  this  way  it  has  been  found 
that  if  the  earth  were  entirely  covered  with  a  blanket  of 
ice  165  feet  thick,  and  the  heat  sent  us  by  the  sun  were 
uniformly  distributed  over  the  ice,  it  would  be  melted 


The  moon  and 
an  arc  light. 


The  Sun.  199 


in  a  year.  An  ice  blanket  of  equal  thickness,  covering 
the  sun,  would  be  melted  off  in  three  minutes.  If  the 
solar  heat  was  dependent  upon  the  combustion  of  coal, 
a  chunk  of  the  best  anthracite  as  big  as  the  moon  would 
have  to  be  fed  to  the  sun  every  forty-five  minutes. 

The  earth  receives  but  a  small  fraction  of  the  light 
and  heat  radiated  by  the  sun.      Imagine  a  hollow  sphere  portionrof  it. 
of  crystal,  the  center  of  which  is  at  the  sun,  the  surface 
of  the  crystal  shell  being  93,000,000  miles  from  the  sun. 
Let  the  earth  be  set,  like  an  emerald,   in  the  crystal  An  emerald  in  a 

J  crystal  sphere. 

shell.  The  amount  of  heat  received  by  the  shell  in  one 
second  equals  that  emitted  by  the  sun  in  the  same  time. 
Remove  the  emerald,  leaving  the  hole  in  which  it  was 
set.  Knowing  the  diameter  of  the  earth,  calculate  the 
area  cut  out  of  the  crystal  shell  by  the  hole  ;  it  is  about 
50,000,000  square  miles.  Also  find  the  area  of  the 
surface  of  the  crystal  sphere. 

As  the  area  of  the  hole  is  to  the  area  of  the  sphere,  so 
is  the  amount  of  heat  received  by  the  earth  in  one 
second  to  that  radiated  by  the  sun  in  the  same  time. 
Substituting  the  proper  numbers  in  this  proportion  we 
find  that  the  sun  radiates  2,200,000,000  times  as  much 
light  and  heat  as  the  earth  receives. 

If  a  javelin  of  ice  forty-five  miles  thick  were  hurled  A  -avelin  of  ice 
directly   at   the   sun    by   some   Titanic   arm,   with   the 
velocity  of  light,  and  the  entire  outpour  of  solar  heat 
were   concentrated    upon   it,    the    threatening   weapon 
would  be  melted  as  fast  as  it  advanced. 

Not  only  do  light  and  heat  come  from  the  sun,  but  Electricai 
electrical  influences  as  well.       In  various  parts  of  the  influences, 
world  are  magnetic  observatories,  where  delicately  sus- 
pended magnets  swing  gently  to  and  fro  in  obedience  to 
changes  of  magnetic  force,  and  vibrate  violently  when 
thrilled  by  magnetic  storms.      In  years  when  sun-spots 


200 


A  Study  of  the  Sky. 


A  notable  mag- 
netic storm. 


A  chrpmq- 
spheric  dis- 
turbance. 


are  numerous,  the  magnetic  needles  are  subject  to 
numerous  large  oscillations,  and  the  glimmering  auroras 
coruscate  in  greatest  splendor.  When  sun-spots  are  few 
the  needles  and  auroras  have  a  comparative  rest. 

There  are  several  instances  where  solar  disturbances 
were  observed  at  times  of  derangement  of  the  earth's 
magnetic  condition. 

On  September  i,  1859,  a  remarkable  magnetic  storm 
was  in  progress.  Earth  currents  played  havoc  with 
telegraphic  communication,  and  were  at  times  sufficiently 
strong  to  work  lines  without  the  aid  of  batteries.  At  a 
station  in  Norway  the  telegraphic  apparatus  was  set  on 
fire.  In  this  country  the  electric  fluid  established  private 
lines  in  the  nervous  systems  of  operators  without  going 
through  the  -formality  of  getting  a  franchise.  The  pen 
of  a  recording  telegraph  in  Boston  was  followed  by  a 
flame.  The  shimmering  auroras  of  the  north  made 
forays  into  the  tropics. 

Late  in  the  forenoon  of  that  day  an  English  astrono- 
mer, who  had  devoted  many  years  to  a  study  of  sun- 
spots,  was  engaged  in  observing  a  large  group  ;  he  was 
startled  by  the  appearance  of  two  brilliant  flashes,  which 
dazzled  his  eye,  though  it  was  protected  by  a  dark  glass. 
In  five  minutes  they  had  faded  away,  having  apparently 
traveled  a  distance  of  35,000  miles  along  the  sun's  disc. 

Professor  Charles  A.  Young,  when  observing  in  the 
Rocky  Mountains  in  1872,  saw,  on  the  morning  of 
August  3  at  8:45,  10:30,  and  11:50,  special  disturbances 
of  the  chromosphere,  caused  by  eruptive  prominences  of 
great  brilliancy.  At  the  same  time  the  magnets  in  Eng- 
lish observatories  twitched.  Professor  Young' s  assistant, 
who  was  making  magnetic  observations,  was  obliged  to 
desist,  because  the  magnet  swung  clear  off  the  scale. 

In  the  face  of  these  and  other  similar  coincidences. 


The  Sun.  201 


one  can  scarcely  doubt  that  solar  disturbances  bear  some 
relation  to  magnetic  storms.  The  nature  of  the  connec- 
tion is  not  known,  and  some  physicists  doubt  whether 
the  electrical  influences  at  work  on  the  sun  are  of  suffi- 
cient intensity  to  cause  such  violent  terrestrial  disturb- 
ances as  are  on  record. 

Various  attempts  have  been  made  to  determine  the  _ 

The  weather. 

effect  of  sun-spots  upon  the  weather.  Meteorological 
records  have  been  diligently  compared  with  those  of  sun- 
spots  to  see  whether  years  when  spots  are  plentiful  are 
hotter  or  cooler  than  those  when  spots  are  few.  The 
results  obtained  by  different  investigators  are  so  conflict- 
ing that  the  question  cannot  be  decided.  An  exhaustive 
study  of  the  amount  of  rainfall  in  different  years  has 
shown  that  fluctuations  probably  exist  resembling  those 
of  sun-spots.  But  much  further  research  has  yet  to  be 
made  before  conclusions  which  command  confidence  can 
be  reached. 

If  sun-spots  had  any  marked  effect  upon  meteorologi- 
cal conditions,  the  commerce  of  the  world  would  be 
affected.  Commercial  crises  have  been  investigated  from 
this  point  of  view,  but  nothing  conclusive  has  been 
determined.  As  the  years  roll  on,  and  both  solar  and 
meteorological  phenomena  are  more  diligently  observed 
than  in  the  past,  some  investigator  may  cause  light  to 
shine  where  darkness  now  reigns  ;  but  enough  has 
already  been  done  to  show  that  commotions  on  the  sun's 
surface  have  very  little,  if  any,  effect  upon  meteorologi- 
cal conditions  on  the  earth. 

The  problem  of  the  maintenance  of  the  sun's  heat  is 

,,  ....          .        .  ,       ,  -IF  The  mainte- 

betore  us.     During  historic  time  the  heat  received  from  nance  of  the 

«  -11  •  T       sun's  heat. 

the  earth  has  been  practically  constant  in  amount.  In 
the  main,  plants  grow  to-day  just  where  the  same  species 
flourished  in  the  days  of  Pliny.  Men  needed  fires  to 


202 


A  Study  of  the  Sky, 


No  observed 
changes. 


Combustion. 


The  meteoric 
theory. 


warm  their  bodies  in  ancient  times  just  as  now,  and  were 
oppressed  by  the  heat  of  midsummer  as  they  are  to-day. 
There  is  no  trustworthy  human  record  of  any  great 
migration  of  animals,  which  might  be  due  to  changes  of 
temperature.  The  rocks,  to  be  sure,  tell  of  great 
changes  in  the  remote  past,  epochs  when  high  northern 
latitudes  experienced  tropical  temperatures,  and  other 
epochs  when  the  temperate  zones  were  encased  in  ice. 
But  no  one  knows  whether  these  conditions  were  due  to 
variations  in  the  earth's  distance  from  the  sun  or  to 
changes  in  the  intensity  of  the  solar  heat  or  to  a  combi- 
nation of  both  causes.  Amazing  as  is  the  daily  outpour 
of  solar  heat,  there  is  no  evidence  from  observation  that 
it  has  changed  in  quantity  or  quality  since  human  history 
began. 

The  supply  cannot  be  infinite  ;  how,  then,  is  the 
radiation  maintained  ?  Not  by  combustion,  for  in 
that  case  the  solar  fires  would  have  burned  out  ages  ago. 
If  the  sun  were  a  mass  of  the  best  hard  coal,  burning  in 
oxygen,  it  would  be  consumed  in  sixty  centuries.  If 
combustion  is  excluded  from  the  list  of  possible  causes, 
what  shall  we  say  about  the  impact  of  bodies  from  with- 
out ? 

If  a  projectile  from  a  rifled  gun  strikes  the  armor- 
plate  of  an  ironclad,  the  shot  is  not  only  deformed  but 
heated.  If  the  earth  should  fall  to  the  sun  from  its  pres- 
ent distance,  as  much  heat  would  be  developed  by  the 
impact  as  the  sun  radiates  in  ninety-five  years.  The  fall 
of  giant  Jupiter  would  cause  an  accession  of  heat  equal 
to  the  amount  now  given  off  in  over  30,000  years.  Why 
may  it  not  be  that  meteoric  bodies  fall  upon  it  in  suffi- 
cient numbers  to  keep  up  the  supply  of  heat?  We  reply 
that  if  there  were  any  such  aggregation  of  meteors  in 
the  sun's  vicinity  it  ought  to  have  a  marked  effect  upon 


The  Sun.  203 


the  motion  of  some  comets  which  come  near  the  sun, 
and  would  encounter  it.  Doubtless  the  sun  receives 
some  heat  from  such  a  source  as  this,  but  only  a  fraction 
of  its  heat  can  be  thus  accounted  for. 

The  theory  generally  accepted  is  called  the  contraction   The  contraction 
theory.     When  a  body  falls  from  any  elevation  to  the  theory- 
earth's  surface,  heat  is  produced  when  it  strikes.      If  the 
same  body  be  attached  to  a  rope  and  made  to  turn  a 
machine  with  badly  oiled  bearings,  at  least  a  portion  of 
the  energy  of  the  descending  body  is  converted  into 
heat.     In  the  first  case  energy  is  converted  into  heat 
suddenly,  at  the  instant  when  the  body  strikes  ;  in  the 
second  case  a  portion  of  the  energy  of  the  descending 
weight  is  being  gradually  converted  into  heat. 

Without  going  more  deeply  into  details  we  may  say 
that  if  the  sun  be  slowly  contracting  in  size,  so  that  the 
particles  of  matter  which  compose  it  are  falling  toward 
the  center,  heat  is  being  produced  by  this  contraction. 

If  the  sun's  diameter  diminishes  five  feet  a  week  the 
total  radiation  of  the  sun  is  explained.  Such  a  shrinkage 
is  so  slight  that  it  would  not  be  certainly  detected  by  our 
present  means  of  astronomical  measurement  in  10,000 
years.  The  contraction  theory  is  considered  the  most 
reasonable  which  has  yet  been  advanced. 

If  all  the  heat  which  the  sun  gives  out  comes  from  its 

.       The  sun's  past 

contraction,  and  it  the  amount  or  heat  radiated  yearly  is  and  future, 
practically  constant  from  age  to  age,  it  is  possible  to 
reason  backward  to  a  time  when  the  sun  was  inconceiv- 
ably vast,  and  to  reason  forward  to  a  time  when  it  will 
probably  cease  to  give  sufficient  heat  to  maintain  human 
life  on  the  earth.  Upon  these  hypotheses  the  sun  would 
consume  18,000,000  years  in  radiating  away  the  heat 
which  would  be  developed  by  its  contraction  from  a  size 
inconceivably  great  to  its  present  dimensions.  Five  mil- 


204 


A  Study  of  the  Sky. 


Contraction. 


Amusing 
speculations. 


lion  years  hence  it  will,  upon  this  hypothesis,  have  only 
half  its  present  diameter,  and  the  matter  composing  it 
will  be  crowded  into  one  eighth  the  space  now  occupied. 
The  compression  will  probably  turn  most  of  it  into  a  liquid 
or  solid  form.  Further  contraction  being  then  very  diffi- 
cult, the  temperature  of  the  sun  will  probably  fall  so 
rapidly  that  its  function  as  a  life-giver  to  the  earth  will 
cease  before  another  5,000,000  years  have  rolled  away. 

Our  reasoning  has  been  based  upon  unverifiable  hy- 
potheses and  the  conclusions  may  be  far  astray.  They 
simply  represent  the  best  guessing  that  scientists  can 
make  with  reference  to  the  past  and  future  of  the  sun. 
There  is  at  any  rate  no  reason  for  alarm  at  present. 

Mark  Twain  has  well  satirized  scientific  speculations 
which  involve  millions  of  years  in  the  following  passage  : 

Now,  if  I  wanted  to  be  one  of  those  ponderous  scientific 
people,  and  "let  on  "  to  prove  what  had  occurred  in  the  remote 
past  by  what  had  occurred  in  a  given  time  in  the  recent  past,  or 
what  will  occur  in  the  far  future  by  what  has  occurred  in  late 
years,  what  an  opportunity  is  here  !  Geology  never  had  such 
a  chance,  nor  such  exact  data  to  argue  from  !  Nor  "  develop- 
ment of  species,"  either  !  Glacial  periods  are  great  things,  but 
they  are  vague,  vague.  Please  observe  :  In  the  space  of  176 
years  the  Lower  Mississippi  has  shortened  itself  242  miles. 
That  is  an  average  of  a  trifle  over  one  and  one  third  miles  per 
year.  Therefore,  any  calm  person,  who  is  not  blind  or  idiotic, 
can  see  that  in  the  old  Oolitic  Silurian  period,  just  a  million 
years  ago  next  November,  the  Lower  Mississippi  was  upwards 
of  1,300,000  miles  long,  and  stuck  out  over  the  Gulf  of  Mexico 
like  a  fishing  rod,  and  by  the  same  token  any  person  can  see 
that  742  years  from  now  the  Lower  Mississippi  will  be  only  a 
mile  and  three  quarters  long,  and  Cairo  and  New  Orleans  will 
have  joined  their  streets  together,  and  be  plodding  comfortably 
along  under  a  single  mayor  and  a  mutual  board  of  aldermen. 
There  is  something  fascinating  in  science.  One  gets  such 
wholesome  results  of  conjecture  out  of  such  a  trifling  invest- 
ment of  fact. 


CHAPTER    XII. 

THE    MOON    AND    ECLIPSES. 

"  That  orbed  maiden,  with  white  fire  laden, 
Whom  mortals  call  the  moon, 
Glides  glimmering  o'er  my  fleece-like  floor, 
By  the  midnight  breezes  strewn." 

—Shelley. 

THOSE   who  speculate  about  the  origin  of  celestial 
bodies  have  a  fine  field  of  thought  in  connection  with  the  earth's 

T  1  rotation. 

the  moon.  It  is  an  undoubted  tact  that  the  moon 
raises  tides  in  our  oceans.  The  wash  of  the  tides 
against  continents  and  islands  tends  to  retard  the  rota- 
tion of  the  earth  by  a  trifling  amount.  If  this  retard- 
ation is  not  offset  by  other  causes,  as,  for  instance,  a 
shrinking  of  the  earth  from  its  progressive  cooling,  the 
length  of  the  day  must  be  gradually  increasing.  The 
increase  must  be  very  slow,  because  it  has  not  yet  been 
brought  to  light  by  observation.  The  action  of  the 
moon  upon  the  earth  is  accompanied  by  a  reaction  of 
the  earth,  which  expresses  itself  in  allowing  the  moon 
gradually  to  move  farther  and  farther  away. 

Reversing  the  process,  we  look  back  through  geologic 
ages  to  a  time  when  the  earth  whirled  much  faster  than  backward. 
at  present,  and  the  moon  was  close  to  its  surface,  both 
bodies  being  hotter  than  now.  How  did  these  bodies 
come  to  be  in  such  close  companionship  ?  Does  it  not 
seem  probable  that  they  were  originally  one  ?  A  grind- 
stone which  rotates  too  rapidly  bursts  asunder.  Is  it 
not  then  entirely  possible  that  when  a  mass  of  heated 

205 


206 


A  Study  of  the  Sky. 


Looking 
forward. 


The  moon's 
rotation. 


matter  in  a  fluid  state  rotates  rapidly,  a  piece  of  it  may 
fly  off? 

If  we  have  hit  upon  a  correct  theory  of  the  moon's 
origin,  let  us  follow  up  the  clue.  The  moon  has  dis- 
engaged itself  from  the  earth,  but  is  still  held  in  check 
by  the  attraction  of  gravity,  so  that  it  is  describing  an 
orbit  about  the  earth.  Both  bodies  are  in  a  fluid  con- 
dition and  rotating.  They  are  so  close  together  that 
the  attraction  of  each  raises  large  tides  on  the  other. 
The  tide  on  the  earth  checks  the  swiftness  of  its 
spinning.  If  the  moon  is  rotating  swiftly  its  tides  put  a 
brake  upon  it.  If,  on  the  other  hand,  it  is  rotating  very 
slowly,  the  friction  of  the  tides  quickens  its  rotation. 

As  previously  mentioned,  one  result  of  this  tidal 
action  is  that  the  two  bodies  separate.  They  grow 
cooler  and  more  rigid  ;  the  powerful  tides  raised  upon 
the  moon  by  the  earth,  keeping  it  continually  egg- 
shaped,  have  had  such  an  effect  upon  the  original  rota- 
tion that  the  moon  has  now  solidified  as  a  slightly 
elongated  body,  the  longest  axis  of  which  points  toward 
the  earth.  So  it  has  come  to  pass  that  the  moon  keeps 
the  same  face  turned  toward  the  earth. 

If  this  be  true,  does  it  rotate  at  all?  Certainly  ;  while 
it  is  making  one  revolution  about  the  earth  it  also 
makes  one  complete  rotation  on  its  axis.  This  may  be 
illustrated  very  simply. 

In  the  center  of  a  circle  one  hundred  yards  in  diame- 
ter a  man  is  standing  ;  he  watches  a  boy  who  runs  at  a 
uniform  rate  around  the  circle  ;  the  boy  keeps  the  left 
side  of  his  head  continually  toward  the  man.  At  one 
instant  the  boy  is  facing  the  north  ;  in  a  few  seconds  he 
has  run  one  fourth  of  the  way  around  the  circle,  and 
faces  westward  ;  in  a  few  seconds  more  he  faces  south- 
ward, then  eastward,  and  finally  northward  again,  when 


The  Moon  and  Eclipses. 


207 


he  has  completed  the  circuit.    Since  the  boy  has  faced  all  A  complete 
points  of  the  compass  successively  he  must  have  turned 
once  around;  but  the  man  has  seen  only  half  of  his  head. 


FIG.  loo.— LUNAR  FORMATIONS. 

If  the  boy  had  slackened  the  speed  of  his  running  at 

Why  we  see 

any  time,  but  kept  on  turning  at  the  same  rate  as  before,    more  than  half 

,  ,11  1-1  r    i  the  moon. 

the  man  would   have  seen  a  little  more  of  his  face  in 


208 


A  Stiidy  of  the  Sky. 


Various 
reasons. 


Some  data. 


The  moon's 
phases. 


consequence.  If  the  boy  had  quickened  his  pace  at 
any  time  without  changing  the  rate  of  his  turning,  the 
man  would  have  gotten  a  view  of  a  little  more  of  the 
back  of  his  head. 

The  moon  is  not  moving  in  a  circle  around  the  earth, 
but  in  an  ellipse  ;  when  it  is  nearest  to  us  it  moves 
more  swiftly  than  when  further  away.  But  it  rotates  on 
its  axis  with  a  constant  speed  :  thus  we  are  enabled  to 
see  a  little  more  than  half  of  its  entire  surface.  Further- 
more the  moon  does  not  stand  upright ;  that  is,  its  axis 
is  oblique  to  the  plane  of  its  orbit.  Consequently  we 
sometimes  see  beyond  its  north  pole,  and  sometimes 
beyond  the  south  pole.  Also,  as  the  earth  turns,  it 
carries  the  observer  along  and  changes  his  point  of 
view,  so  that  he  can  see  a  trifle  more  of  the  moon  than 
otherwise.  Fifty-nine  per  cent  of  the  moon's  entire 
surface  is  thus  presented  to  our  view.  The  visible  area 
is  slightly  more  than  double  that  of  Europe. 

The  moon's  diameter  is  2,163  miles,  and  its  average 
distance  from  us  is  238,840  miles.  It  is  A  as  large  as 
the  earth,  but  only  *V  as  heavy. 

The  moon's  apparent  changes  of  form  result  from  its 
revolution  around  the  earth,  which  is  accomplished  in 
27^  days.  If  it  is  to-day  nearly  on  a  line  between  the 
earth  and  the  sun,  it  will  not  be  in  line  again  at  the 
expiration  of  this  period  of  time.  For  the  earth  has 
moved  on  meanwhile  and  altered  the  direction  of  the 
line.  Thus  it  comes  to  pass  that  29^/2  days  elapse 
before  the  moon  crosses  the  line  again. 

Why  then  is  not  the  sun  hidden  from  view  once  every 
29^  days  by  the  interposition  of  the  moon's  dark  mass? 
The  moon's  orbit  is  tilted  in  such  a  way  that  the  moon 
usually  passes  apparently  above  or  below  the  sun, 
instead  of  in  front  of  him.  When  the  moon  is  nearly  in 


The  Moon  and  Eclipses.  209 

line  between  the  sun  and  us,  the  sun  lights  up  that  half 
of  it  which  is  turned  away  from  us,  and  the  dark  side  is 
toward  us.  Besides  this,  the  sun  blinds  our  eyes,  so 
that  we  can  see  nothing  in  his  immediate  neighborhood 
unless  it  be  intensely  bright.  The  moon  is  "  new." 

But  in  a  couple  of  days  our  vision  will  be  charmed  by 
the  sight  of  the  young  moon  hanging  low  in  the  west  in 
the  evening  twilight.  Its  position  with  reference  to  the 
sun  has  so  changed  that  we  can  see  a  part  of  its  bright 
hemisphere,  as  a  graceful  crescent. 

Most  of   the  dark  hemisphere  of  the  moon   is  also   _. 

1  f  Eaith  shine. 

visible.  The  earth  plays  the  part  of  a  mirror,  and 
reflects  back  a  portion  of  the  sunlight  which  it  receives. 
Some  of  this  reflected  sunlight  lights  up  the  dark  side 
of  the  moon,  so  that  we  can  see  it. 

On  the  next  night  the  moon  is  east  of  its  former  posi-   , 

First  quarter. 

tion,  and  sets  later  ;  its  crescent  is  larger.  A  week 
after  new  moon  comes  the  phase  of  first  quarter,  when 
the  moon  is  a  bright  semicircle  off  in  the  south  at  sun- 
set. On  that  evening  and  the  three  following  its 
telescopic  appearance  is  the  most  interesting. 

From  night  to  night  the  illuminated  disc  grows  larger, 

'     Full  moon. 

as  the  moon  moves  eastward,  till  it  becomes  a  complete 
circle,  and  the  moon  is  full.  It  then  rises  about  sunset 
and  sets  about  sunrise. 

During  the  next  week  the  moon  wanes  and  shrinks  to 

.    .      ,  Last  quarter. 

a  semicircle.  One  may  then  see  it  in  the  south  at  sun- 
rise, and  in  the  southwest  during  the  forenoon  ;  it  is  at 
the  last  quarter.  The  half  moon  changes  to  a  diminish- 
ing crescent,  and  is  lost  in  the  sun's  rays,  as  it  becomes 
new  again. 

When  the  moon  is  full,  large  dark  brown  areas  are 

The  face  of  the 

seen  upon  its  face  with  the  naked  eye.     According  to  f"u  moon. 
Alexander  von  Humboldt  the  people  of  Asia  Minor  see 


210 


A  Study  of  the  Sky. 


in  these  markings  a  resemblance  to  terrestrial  seas  and 
continents,  and  say  that  the  moon  exhibits  a  reflection 
of  the  earth  as  though  it  were  a  mirror.  In  the  minds 
of  many  a  human  figure  is  outlined  ;  it  has  been  super- 
judas  iscariot.  stitiously  asserted  that  it  is  the  figure  of  Judas  Iscariot, 

whose  sin  has  led 
to  his  being  thus 
pilloried  before 
the  eyes  of  man- 
kind for  all  gen- 
erations. The 
casual  onlooker 
perceives  a  hu- 
man face,  the 
eyes,  nose,  and 
mouth  being 
fairly  conspicu- 
ous. Even  chil- 
dren notice  it. 

An  opera-glass 
shows  that  the 
bright  portions 
of  the  lunar  sur- 
face are  covered 
with  rugged  for- 
mations, while 
the  dark  portions 

FIG.  101. — LUNAR  PLAINS,  CALLED  SEAS.  are      Smooth. 

When  Galileo's  telescope  revealed  these  smooth  regions 
The  plains.  tnev  were  supposed  to  be  seas,  which  soon  received 
such  names  as  the  Sea  of  Serenity,  the  Ocean  of  Tem- 
pests, and  the  Lake  of  Death.  More  powerful  instru- 
ments show  minute  pits  sunken  all  over  the  supposed 
seas  ;  they  are  therefore  vast  plains. 


The  Moon  and  Eclipses.  211 

Great  hopes  were  originally  entertained  that  with 
increase  of  telescopic  power  would  come  evidences  that 
the  moon  was  inhabited  by  intelligences,  whose  works 
would  become  manifest.  It  is  doubtful  whether  any 
telescope  that  has  already  been  constructed,  or  ever  will 
be,  can  show  the  moon' s  surface  better  than  it  would  be 
seen  with  the  unassisted  eye  at  a  distance  of  200  miles. 
A  structure  as  large  as  the  Liberal  Arts  Building  at  the 
World's  Fair  would  be  readily  made  out,  if  of  a  different 
color  from  the  soil  on  which  it  was  built.  No  details  of 
the  architecture  could  be  distinguished,  and  one  would 
never  know  whether  it  was  a  formation  of  nature  or  a 
structure  erected  by  intelligent  beings.  Herschel  once 
used  a  magnifying  power  of  7,000  diameters,  which 
would  theoretically  bring  the  moon  within  thirty-five 
miles,  but  he  could  not  see  as  well  as  if  he  had  used  a 
much  lower  amplification,  because  of  ever-present  at- 
mospheric disturbances. 

Despite  this  atmospheric  handicap  a  vast  amount  of 

.  Accuracy  of 

lunar  detail  has  been  studied  out,  so  that  the  topog-   lunar  maps, 
raphy   of    the   side   of    our    satellite   which    is   turned 
toward  us  is  much  better  known  than  that  of  vast  areas 
of  the  earth's  surface. 

For  the  geographical  explorer  has  to  press  his  way 
through  deadly  swamps,  and  across  torrid  deserts, 
.scorched  to  the  marrow  by  the  sun,  smitten  by  nameless 
fevers,  tormented  by  insects,  menaced  by  wild  beasts, 
and  ambushed  by  savages.  The  astronomer,  on  the 
other  hand,  sits  in  the  seclusion  of  his  observatory,  in 
the  quiet  of  a  beautiful  evening,  making  his  measure- 
ments with  inoffensive  spider-webs,  and  recording  them 
with  a  harmless  pencil. 

The  chief  classes  of  lunar  formations  are  craters,  moun-    . 

A  summary. 

tain  ranges,  isolated  peaks,  plains,  rays,  clefts,  and  rills. 


212 


A  Study  of  the  Sky. 


The  crater 
Copernicus. 


Other  craters. 


A  drop  of  water  falling  from  the  eaves  of  a  house 
upon  soft  moist  earth  below  makes  a  depression  sur- 
rounded by  a  little  wall  of  mud ;  this  resembles  a  lunar 
crater. 

One  of  the  finest,  situated  not  far  from  the  center  of 
the  full  moon,  is  named  Copernicus  (Fig.  102) ;  it  is  fifty- 
six  miles  in  diameter.  To  compare  Vesuvius  with  it  is 
to  compare  a  pin-prick  with  a  silver  half  dollar.  In  the 
center  of  the  ring  lies  a  rugged  hill  half  a  mile  high,  lifting 
its  six  heads  up  into  the  sunlight.  The  surrounding  ring 
is  beautifully  terraced,  as  if  there  had  been  successive 
elevations  and  subsidences  of  lava  in  ages  past.  The 
summit  of  the  ridge  is  a  narrow  ring,  the  top  of  which 
is  over  two  miles  above  the  floor  of  the  crater.  The 
surrounding  region  is  thickly  dotted  with  minute  crater- 
lets.  When  the  sun  rises  upon  this  magnificent  crater 
the  highest  parts  of  the  ring  catch  the  sunbeams  and 
outline  the  majestic  circle.  Within  all  is  dark  ;  the  sun 
rises  higher  and  its  light  begins  to  creep  down  the  inner 
wall  of  the  further  side  of  the  crater.  Yet  all  is  dark 
within,  and  the  central  hill  is  invisible.  Presently  the 
six  central  peaks  emerge  one  by  one  from  the  surround- 
ing darkness,  and  one  can  dimly  descry  the  floor  of  the 
crater  still  enveloped  in  shadow,  but  rendered  faintly 
visible  by  the  light  reflected  from  the  illuminated  portion 
of  the  inner  wall.  Hours  wear  away,  and  the  interior  is 
bathed  in  sunshine,  except  where  short  shadows  hug  a 
portion  of  the  crater  wall  and  nestle  at  the  foot  of  the 
central  hill. 

A  few  of  the  largest  craters  are  over  one  hundred 
miles  in  diameter.  In  some  cases  the  floors  of  craters 
are  depressed  below  the  general  level  of  the  surface  ;  in 
other  cases  the  floors  are  elevated.  It  may  be  quite 
smooth,  or  it  may  be  pitted  with  tiny  craters  and  orna- 


The  Moon  and  Eclipses. 


213 


mented  with  rugged  hills.     The  walls  may  be  precipi- 
tous in  the  extreme,  or  magnificently  terraced  and  cut 


FIG.  102.— COPERNICUS. 


up  by  yawning  ravines.      A  man  standing  in  the  center 

of  Schickard   could   not  see  the   rampart   surrounding  Schickard. 

him,  though  it  is  over  10,000  feet  high  ;  so  rapidly  does 


214 


A  Study  of  the  Sky. 


The 
Apennines. 


Pico. 


The  plains. 


Rays. 


the  moon's  surface  curve,  because  of  its  small  diameter, 
that  the  top  of  the  rampart  would  be  below  the  man's 
horizon.  One  of  the  peaks  within  Clavius  rises  nearly 
five  miles  above  the  bottom  of  one  of  the  craterlets  at  its 
foot.  Sunlight  never  reaches  the  bottoms  of  some  of 
the  pits  near  the  moon's  poles. 

The  finest  mountain  range  is  the  Apennines  (Fig. 
103).  It  is  only  450  miles  long,  but  the  summits  of  its 
peaks  rise  to  altitudes  which  rival  those  of  the  Andes. 
The  loftiest  peak  lifts  its  head  to  the  proud  height  of 
18,500  feet.  On  one  side  the  entire  range  rises  gradually 
from  the  plain  ;  on  the  other  side  it  descends  precipi- 
tously to  the  border  of  a  "sea."  The  shadows  cast  by 
some  of  these  peaks  when  the  sun  shines  upon  them  are 
over  75  miles  in  length.  The  heights  of  mountains  and 
of  crater-rims  are  found  by  measuring  the  lengths  of 
their  shadows. 

Isolated  mountains  are  rather  rare.  One  of  the  finest 
is  named  Pico.  Like  the  spire  of  some  buried  cathe- 
dral it  rises  abruptly  from  a  level  plane  to  a  height  of  a 
mile  and  a  half.  A  most  imposing  spectacle  it  would  be 
to  a  man  standing  near  its  base. 

The  great  lunar  plains,  which  have  already  been 
partially  described,  and  which  look  quite  smooth  when 
viewed  with  a  small  telescope,  lose  their  unruffled 
appearance  when  examined  with  a  high  magnifying 
power.  The  surface  is  covered  with  low  ridges,  and 
minute  pits  abound. 

Several  of  the  larger  craters  are  surrounded  by  fine 
systems  of  diverging  rays,  which  are  distinct  at  full 
moon.  Tycho,  a  noble  crater,  the  wall  of  which  is 
17,000  feet  high  and  fifty-four  miles  in  diameter,  is  the 
center  of  the  most  conspicuous  system  of  rays  to  be 
seen  on  the  moon.  It  looks  like  the  hub  of  a  wagon 


The  Moon  and  Eclipses. 


215 


Clefts. 


Rills. 


wheel,  from  which  the  spokes  radiate  in  all  directions. 
The  rays  are  whiter  than  the  general  surface  and  are 
often  hundreds  of  miles  in  length. 

Clefts  are  cracks  which  appear  in  various  regions. 
They  are  half  a  mile  or  so  in  width,  and  run  in  some  in- 
stances hundreds  of  miles  across  plains  and  through 
craters,  never  halting  at  any  obstacle.  They  are  of 
unknown  depth.  Such  a  chasm  upon  the  earth  would 
strike  terror  to  the  heart  of  a  traveler  who  found  it 
lying  across  his  path. 

Rills  resemble  the  beds  of  ancient  water  courses; 
they  are,  however,  small,  and  not  likely  to  catch  the 
eye  of  the  casual  gazer. 

A  body  which  was  once  hot  and  has  cooled  may  well 
exhibit  most  of  the  peculiar  formations  which  have  just  the  formations. 
been  described.  Most  of  them  have  counterparts  upon 
the  earth.  The  neighborhood  of  the  terrestrial  crater 
Vesuvius  is  similar  in  appearance  to  many  a  portion  of 
the  lunar  landscape.  The  craters  cannot  be  closely 
likened  to  terrestrial  volcanoes.  The  latter  have  small 
throats,  and  are  surrounded  by  outpourings  of  lava. 
The  former  frequently  embrace  hundreds  and  even 
thousands  of  square  miles  within  their  walls,  and  do  not 
appear  to  have  deluged  the  surrounding  country  with 
the  products  of  fiery  outbreaks.  The  systems  of  rays 
can  scarcely  be  due  to  overflows  of  lava.  For  in  that 
case  a  ray  would  spread  out,  the  further  it  got  from  the 
parent  crater  ;  it  would  also  be  deflected  when  it  en- 
countered another  crater,  and  would  be  either  heaped 
up,  or  would  flow  around  it.  But  the  rays  are  un- 
changed in  width  as  they  take  their  way  across  moun- 
tains and  through  craters. 

The  general  appearance  of   the  lunar  crust  may  be    Ta  _cinder 
reproduced  on  a  small  scale  by  pouring  the  tap-cinder 


FIG.  103.— THE  APENNINES. 
216 


The  Moon  and  Eclipses.  217 

from  a  smelting  furnace  into  a  stout  receptacle.  At  first 
a  thin  crust  forms  where  the  mass  is  exposed  to  the  cool- 
ing action  of  the  air.  The  crust  is  broken  open  in 
various  spots  by  the  action  of  the  heated  fluid.  Some 
of  the  molten  matter  exudes  through  the  holes  ;  a  little 
ring  is  built  up,  or  a  cone-like  structure.  The  contract- 
ing material  within  leaves  the  crust  without  adequate 
support  and  it  cracks  in  weak  places.  Thus  the  work  of 
solidification  proceeds,  and  the  final  appearance  of  the 
crust  bears  a  resemblance  to  the  lunar  surface. 

The  question  of  changes  in  lunar  topography  during 
the  past  hundred  years  is  a  mooted  one.  Certain  it 
is  that  there  have  been  no  marked  changes.  But 
there  may  have  been  minor  ones,  such  as  the  falling 
of  a  portion  of  the  wall  of  a  crater,  or  the  crumbling 
of  some  pinnacle.  There  is  no  trustworthy  evidence 
of  any  volcanic  outburst,  great  or  small.  Such  an 
eruption  as  that  at  Krakatoa,  which  in  1883  gave  rise 
to  the  red  glows  which  persisted  for  many  months,  could 
not  have  escaped  the  scrutiny  of  astronomers.  Craters 
change  their  appearance  greatly  as  the  sun  rises  upon 
them  and  causes  their  shadows  to  shift;  hence  very  care- 
ful and  prolonged  study,  comparing  the  old  maps  with 
present  appearances,  is  needed  to  establish  any  claim  of 
change.  Now  that  photography  has  entered  the  field, 
and  the  sensitive  plates  make  a  record  which  is  free 
from  bias,  it  may  be  possible  in  the  future  to  attain  a 
good  degree  of  certainty  in  this  matter. 

When  the  moon  parted  company  with  the  earth,  ages  Thelunar 
ago,  it  is  probable  that  both  masses  were  enwrapped  in  a  atmosphere, 
gaseous  envelope.     The  lion's  share  of  this  atmosphere 
naturally  fell  to  the  earth,  because  of  its  superior  attract- 
ive power.     The  moon  may   have   started   away   with 
quite  a   scanty  covering  of  air.     It  is  natural  then  to 


218 


A  Study  of  the  Sky. 


A  star  is 
hidden. 


Effect  pf 
refraction. 


A  vacuum. 


suppose  that  the  moon's  atmosphere  is  now  very  rare. 
So  clearly  are  the  lunar  mountains  denned,  so  black  are 
their  shadows,  so  sharp  is  the  dividing  line  between  the 
illuminated  and  unilluminated  portions  of  the  moon, 
that  there  cannot  be  a  dense  envelope  of  air,  which  be- 
haves as  ours  does,  scattering  the  sunlight  in  every  direc- 
tion from  the  motes  which  float  about  in  it,  and  causing 
twilight  as  the  sun  rises  or  sets.  But  a  more  delicate 
test  is  at  hand. 

As  the  moon  performs  its  monthly  journey  around  the 
sky  it  passes  between  us  and  countless  stars  which  seem 
to  bestrew  its  pathway,  but  are  really  far  beyond  it  in 
the  depths  of  space.  So  well  is  the  moon's  rate  of  travel 
known  that  astronomers  can  predict  accurately  the  time 
when  it  will  hide  any  particular  star  from  view.  If 
there  were  a  lunar  atmosphere  a  star' s  radiance  would 
be  dimmed  just  before  it  disappeared  ;  it  would  also 
change  color  as  the  sun  does  at  sunset,  when  it  shines 
through  a  greater  thickness  of  air  than  at  noon. 

The  mention  of  sunset  brings  to  mind  the  fact  that  the 
air  has  a  refractive  power  and  bends  rays  of  light  which 
pass  through  it.  On  this  account  we  see  the  sun  after  it 
is  really  below  the  astronomical  horizon,  and  it  appears 
again  the  next  morning  before  it  would,  were  there  no 
air  to  bend  its  rays  out  of  a  straight  course. 

A  lunar  atmosphere  would  therefore  bend  the  rays  of 
light  from  a  star,  and  delay  the  time  of  its  disappearance 
just  as  our  air  delays  the  time  of  sunset.  It  would  also 
cause  the  star  to  reappear  before  it  would  otherwise. 
Thousands  of  occultations  of  stars  by  the  moon  have 
been  accurately  observed.  The  stars  disappear  and  re- 
appear on  time. 

The  vacuum  at  the  lunar  surface  is  believed  to  be  as 
complete  as  under  the  exhausted  receiver  of  an  air-pump. 


The  Moon  and  Eclipses. 


219 


What  has  become  of  the  original  aerial  endowment 
which  the  moon  probably  possessed  ?     Several  theories 
have  been  given  to  explain  its  disappearance.     The  best 
of  these  is  based  upon  observations  on  terrestrial  rocks  ; 
a  rock  which  is  heated  expels  gases  which  it  had  pre- 
viously absorbed  ;  when  cooling,  it  has  the  power  to  take 
them  up  again. 
It  may  be  that 
the  lunar   at- 
mosphere en- 
tered into  chem- 
ical combination 
with  the  cooling 
rocks,  and  our 
satellite    was 
thus  stripped  of 
its  aerial  ves- 
ture. 

No  water  is  di- 
rectly   revealed 
by   telescopic 
search  ;  if  it  ex- 
isted   the    sun 
would  evapo- 
rate it,   and  a 
slight  lunar  at- 
mosphere, COm-  FlG-  I04--THE  MARE  CRISIUM. 
posed  of  water  vapor,  would  be  formed.     Since  obser- 
vation has  pronounced  against  the  existence  of  a  lunar  water, 
atmosphere  of  appreciable  density,  it  has  also  negatived 
the  existence  of  water  upon  the  moon's  surface.     Small 
bodies  of  ice  may  be  there  undetected,  but  there  is  no 
cogent   reason   for   believing   in  their  existence.      Any 
water  which  the  moon  possessed  originally  may  have 


220 


A  Study  of  the  Sky. 


A  hot -bed. 


Air  as  a  blan- 
ket. 


The  temper- 
ature. 


been  taken  up  by  the  rocks  as  they  crystallized,  or  may 
have  sunk  into  cavernous  depths  in  the  interior. 

The  absence  of  air  has  a  marked  effect  upon  the  tem- 
perature at  the  moon's  surface.  The  gardener's  hot-bed 
illustrates  this  matter.  The  sunlight  pours  through  the 
glass  cover  of  the  bed  and  warms  the  soil  within.  The 
soil  in  turn  strives  to  radiate  off  the  heat  which  it  has 
received,  but  the  glass  is  a  barrier  to  the  returning  heat. 
For  heat  from  an  intensely  heated  body  passes  through 
glass  quite  readily,  while  heat  from  a  body  at  a  low  tem- 
perature, like  the  earth,  finds  difficulty  in  passing 
through  glass.  Therefore  the  gardener's  bed  becomes 
considerably  warmer  than  the  exposed  ground  round 
about  it. 

In  the  same  way  our  atmosphere  keeps  in  the  heat 
which  the  sunbeams  have  brought  to  the  earth' s  surface  ; 
the  earth  is  kept  warm  by  its  blanket  of  air.  For  this 
reason  the  mean  temperature  on  the  top  of  a  high  moun- 
tain is  much  lower  than  that  at  its  foot ;  the  top  is  cov- 
ered by  a  scantier  blanket  of  air  than  the  foot.  Aero- 
nauts ascending  to  great  heights  experience  bitter  cold. 
Twenty  miles  above  the  earth's  surface  the  temperature 
must  be  appallingly  low.  Were  the  atmosphere  to  be 
taken  away,  the  sun  would  beat  upon  us  more  hotly 
than  at  present,  but  the  beneficent  heat  would  be  quickly 
radiated  off,  and  eternal  winter  would  reign. 

Many  attempts  have  been  made  to  determine  the  tem- 
perature of  the  moon's  surface  by  measurement  of  the 
heat  which  it  sends  to  us.  The  moon's  rays,  condensed 
at  the  focus  of  a  large  mirror,  fall  upon  a  delicate  in- 
strument for  measuring  changes  of  temperature. 
Though  the  results  of  various  experiments  differ,  it  is 
considered  quite  certain  that  the  warmest  portions  of  the 
lunar  surface  never  rise  above  the  temperature  of  freez- 


The  Moon  and  Eclipses.  221 

ing  water.  When  some  point  has  been  in  darkness  for 
a  week  or  more,  the  lunar  nights  being  over  two  weeks 
in  length,  its  temperature  can  scarcely  be  above  — 200° 
Fahrenheit.  It  has  been  estimated  that  the  sun  sends 
to  the  earth  as  much  heat  in  a  minute  as  the  full  moon' 
would  give  could  it  shine  upon  us  for  three  years  without 
change  of  phase. 

The  moon  is  a  land  of  death,  the  sepulcher  of  any  life    , 

1  A  visit  to  the 

which  may  once  have  existed  upon  it.  If  an  astronomer  moon- 
could  establish  his  telescope  upon  the  rim  of  some  great 
crater  during  a  lunar  night,  and  could  endure  the  rigor 
of  the  cold,  as  well  as  the  absence  of  air,  what  glories 
would  rivet  his  astonished  vision  !  The  sky,  blacker 
than  the  deepest  velvet,  is  inlaid  with  jewels  unmatched 
by  the  gleam  of  a  Koh-i-noor,  or  the  splendid  glow  of 
the  precious  ruby.  Each  of  the  familiar  constellations 
shines  forth  with  a  brilliancy  before  unknown.  Not  a 
star  scintillates  ;  all  shine  serene,  as  though  some  high 
behest  were  upon  them.  A  crowd  of  smaller  stars, 
never  before  revealed  to  the  unaided  eye,  besprinkle 
the  sable  folds  of  the  garment  of  night.  The  Milky  Way 
enchants  the  beholder  by  its  splendor.  Surely  the  char- 
iot of  the  Almighty  has  been  driven  along  it. 

Amid  this  unchanging  calm  there  is  one  magnificent 
panorama.  Yonder  glows  a  mighty  orb,  which  moves  panorama, 
with  majestic  pomp  amid  the  hosts  of  heaven  ;  star  after 
star  is  quenched  before  it,  and  reappears  in  its  wake. 
Steadily  the  sunlight  creeps  over  its  surface,  changing 
it  from  a  crescent  to  a  full-orbed  circle.  While  this 
change  is  taking  place  what  a  panorama  rolls  before  the 
astronomer's  eye,  and  is  eagerly  viewed  with  his  tele- 
scope !  Great  masses  of  white  cloud,  tinged  with  golden 
orange,  vast  expanses  of  ocean,  dull  continents  relieved 
here  and  there  by  a  dash  of  color,  snowy  masses  at  the 


222 


A  Study  of  the  Sky. 


The  day  comes. 


The  day 
declines. 


poles — all  these  roll  before  him,  now  glowing  in  the 
light,  now  lost  in  the  darkness. 

But  what  is  the  soft  radiance  which  appears  yonder 
upon  the  horizon?  Higher  and  higher  it  rises  ;  more 
and  more  is  the  lunar  landscape  lighted  up.  The 
ghostly  shapes  of  distant  mountains  are  dimly  outlined. 
Long,  black  fingers  stretch  themselves  across  the 
plains  ;  thousands  of  dark  pits  dot  the  ashen  landscape. 
The  sun's  long  coronal  streamers  are  heralding  the 
dawn.  Thoughtlessly  he  watches  for  the  twilight,  and 
expects  to  see  the  Milky  Way  veil  its  glories  before  the 
coming  of  the  king  of  day  ;  but  it  shines  on,  with 
undiminished  splendor.  Behind  him,  on  the  opposite 
side  of  the  crater,  towers  a  precipitous  pinnacle.  Its 
rugged  summit  catches  a  ray  of  direct  sunlight  and  is 
bathed  in  its  effulgence.  Yonder  glows  another  peak 
and  still  another  against  the  jet  black  sky.  No  rosy 
tints  melt  into  amber,  and  suffuse  the  heavens.  No 
lark  soars  to  greet  the  rising  sun,  or  to  pour  out  his  soul 
in  ecstatic  song.  The  silver-rimmed  crater,  standing  on 
the  dividing  line  between  the  world  of  light  and  the 
world  of  darkness,  is  filled  with  the  shadow  of  its  own 
wall.  Deep  down  in  its  rugged  depths  are  descried  the 
heads  of  its  central  mountain,  which  are  soon  to  be 
kissed  by  the  sunlight.  No  laughing  brook  leaps  down 
the  mountain  side  ;  no  morning  zephyr  plays  among 
the  rugged  battlements  ;  no  flower  turns  its  charming 
face  toward  the  sun. 

The  day  wears  on  ;  the  somber  shadows  move  over 
the  desolate  wilds.  The  rocky  sentinels  keep  their 
grim  and  silent  watch  over  the  dead  planet.  Stray 
meteors  dash  against  the  beetling  crags,  or  bury  them- 
selves in  the  plains  beneath.  The  life-giving  sunbeams 
find  no  life  responsive  to  their  subtle  touch.  The 


The  Moon  and  Eclipses. 


223 


shadows  turn  and  lengthen  ;  the  glowing  sun  sinks 
beneath  the  horizon,  and  the  dread  chill  of  the  long 
lunar  night  comes  on. 

The  moon  is  of  service  to  man  in  many  ways.  Its 
light  relieves  the  darkness  of  the  night,  and  this  adds  to 
his  safety  and  happiness.  As  it  moves  across  the  face 
of  the  sky  it  becomes  a  timekeeper  by  which  the 
mariner  may  determine  his  longitude,  in  case  he  is  on  a 
long  voyage  and  fears  that  the  error  of  his  chronometer  The  mariner. 


FIG.  105. — A  RUGGED  REGION  NEAR  TYCHO. 

is  not  known  accurately.  For  the  ' '  Nautical  Almanac' ' 
gives  the  distance  of  the  moon  from  certain  bright  stars 
at  given  Greenwich  times,  each  day  of  the  year.  The 
mariner  measures  one  or  more  of  these  distances  with  a 
sextant,  and  thus  determines  the  true  Greenwich  time. 

The  moon  is  the  chief  agent  in  the  production  of  the  The  t}des 
tides,  which  at  their  flood  lift  ships  over   harbor  bars 


224 


A  Study  of  the  Sky. 


Chronology. 


The  ruse  of 
Columbus. 


Superstitions. 


and  bear  them  to  the  wharves.  Without  the  tides  the 
city  of  Liverpool  would  lose  its  commerce.  Its  harbor 
communicates  with  the  ocean  by  a  narrow  neck,  through 
which  600  million  tons  of  water  rush  out  every  six  hours 
during  the  ebb  of  the  tide,  scouring  the  channel,  and 
carrying  off  the  silt  and  debris  which  would  otherwise 
choke  it. 

Eclipses  either  of  the  sun  or  the  moon,  which  occurred 
at  the  times  of  notable  events,  have  given  much  assist- 
ance to  historians  in  threading  the  mazes  of  ancient 
chronology.  The  lunar  eclipse  of  March  13  in  the  year 
3  B.  C.  took  place  at  the  death  of  Herod,  and  thus 
serves  to  determine  the  date  of  the  birth  of  Christ. 
Another  eclipse  has  been  employed  to  rectify  the  first 
year  of  the  reign  of  Cyrus  of  Babylon. 

Columbus  made  use  of  the  lunar  eclipse  of  March  i, 
1504,  to  obtain  much-needed  supplies  for  his  men.  The 
inhabitants  of  Jamaica  refused  to  give  them  to  him,  and 
he  threatened  to  take  away  the  moon's  light  should 
they  persist  in  their  determination.  When  the  eclipse 
came  on,  the  savages  were  struck  with  terror  and  has- 
tened to  supply  his  wants. 

There  have  been  many  superstitions  connected  with 
the  moon,  some  of  which  flourish  even  to-day  in  rural 
communities.  Their  absurdity  is  their  sufficient  refuta- 
tion. 

It  has  been  said  that  the  moon  produces  blindness  by 
shining  upon  a  sleeper's  eyes  ;  that  it  fixes  the  hour  of 
death,  which  occurs  at  the  change  of  tide  ;  that  cucum- 
bers, radishes,  and  turnips  increase  at  full  moon  ;  that 
onions  thrive  best  after  the  moon  has  passed  its  full  ; 
that  herbs  gathered  before  full  moon  are  of  greatest 
efficacy  ;  that  vines  trimmed  at  night  when  the  moon  is 
in  the  sign  of  the  Lion  are  safe  from  field  mice  and 


The  Moon  and  Eclipses.  225 

other  pests  ;  that  potatoes  are  best  planted  at  a  certain 
time  of  the  moon  ;  that  shingles  will  curl  up  if  not  laid 
at  the  right  phase  of  the  moon,  etc.,  etc. 

Especially  persistent  are  those  ideas  which  connect 
the  moon  with  the  weather.^    A  change  of  lunar  phase  " 


is  said  to  be  connected  with  a  change  of  weather  ;  since 
the  moon  changes  its  phase  every  week,  every  change 
of  the  weather  must  occur  within  four  days  of  a  change 
of  phase.  People  who  watch  for  such  changes  are  will- 
ing to  wait  more  than  four  days,  if  necessary,  for  the 
weather  to  accommodate  itself  to  the  moon.  "Wet" 
and  '  '  dry  '  '  moo*ns  are  carefully  watched  for  by  farmers 
throughout  the  country.  When  the  crescent  moon 
hangs  low  in  the  west  soon  after  sunset,  if  a  line  joining 
the  two  cusps  is  nearly  horizontal,  so  that  the  moon  can 
apparently  hold  water,  it  is  a  "dry  moon."  If  the 
line  joining  the  cusps  be  tipped  up  at  a  very  marked 
angle,  so  that  the  moon's  crescent  cannot  hold  water, 
the  moon  is  called  '  '  wet.  '  '  The  position  of  the  cusps 
of  the  moon  can  be  predicted  for  thousands  of  years  to 
come,  but  no  one  can  foretell  the  weather  a  week  ahead. 
The  full  moon  is  said  to  clear  away  clouds  ;  it  is  hard  ~. 

*  Clouds  cleared 

to  see  how  a  body  which  sends  us  so  minute  a  quantity  away- 
of  heat  can  have  any  appreciable  effect  upon  the  clouds. 
Perhaps  by  showing  their  thinness,  and  making  plain 
the  rifts  which  exist  in  them,  the  moon  gets  the  credit 
of  thinning  them. 

That  small  variations  in  the  position  of  the  magnetic  Magnetic 
needle  take   place,    as   the   moon   approaches  and  re-   effects- 
cedes,   in  pursuing  its  elliptical  orbit,   is  admitted. 

ECLIPSES. 

Eclipses  of  the  moon  occur  when  it  plunges  into  the  The  eanh,s 
shadow  of  the  earth.     If  the  sun  were  of  the  same  size  shadow. 


226  A  Study  of  the  Sky. 

as  the  earth,  the  shadow  of  the  latter  would  be  a 
cylinder,  about  8,000  miles  in  diameter,  stretching  out 
to  an  infinite  distance.  But  as  the  sun  is  much  larger 
than  the  earth,  the  shadow  is  tapering.  Its  length 
varies  somewhat,  since  the  earth  is  sometimes  farther 
away  from  the  sun  than  at  others.  Its  average  length  is 
857,000  miles,  and  its  average  thickness,  at  the  point 
where  the  moon  encounters  it,  is  5,700  miles.  The 
moon  often  merely  dips  a  little  way  into  the  shadow, 
and  suffers  only  a  partial  eclipse.  Being  only  2,163 
miles  in  diameter,  it  is  readily  totally  eclipsed,  and  may 
remain  immersed  in  the  shadow  for  two  hours. 

Since  the  moon  moves  eastward,  its  eastern  edge, 
A  lunar  eclipse,  which  is  at  the  left  hand  as  one  faces  it,  strikes  the 
shadow  first ;  a  circular  notch  then  seems  to  be  eaten 
out  of  the  moon's  edge,  much  as  if  it  were  an  apple  out 
of  which  a  boy  had  taken  a  bite.  The  notch  increases 
till  the  lunar  disc  is  overspread  with  shadow,  but  the 
moon  does  not  usually  disappear.  The  solid  body  of 
the  earth  casts  a  shadow  sufficiently  dense  to  blot  the 
moon  out  as  completely  as  if  it  were  annihilated,  but  the 
transparent  coating  of  air  which  the  earth  carries  assists 
the  moon  in  its  otherwise  gloomy  experience.  Many 
rays  of  sunlight  pierce  this  transparent  medium,  are 
bent  by  it  out  of  their  otherwise  straight  course,  and  fall 
upon  the  moon,  illuminating  it  rather  dimly  because  they 
have  been  enfeebled  by  passing  through  our  atmosphere. 
They  have  also  acquired  the  sunset  tinge,  and  give  the 
moon  a  coppery-red  hue.  If  clouds  stop  these  rays, 
the  moon  vanishes  entirely  ;  if,  on  the  other  hand,  the 
portion  of  the  atmosphere  traversed  by  them  is  excep- 
tionally free  from  moisture,  the  lunar  disc  is  lighted  up 
so  strongly  that  persons  unaware  of  the  eclipse  simply 
wonder  why  the  moon  is  not  as  bright  as  usual.  After  a 


228 


A  Study  of  the  Sky. 


The  moon' 
shadow. 


A  solar  eclipse. 


while  the  eastern  edge  of  the  moon  emerges  into  sun- 
light and  the  shadow  is  gradually  left  behind. 

Since  the  moon's  diameter  is  a  little  more  than  one 
fourth  that  of  the  earth,  and  their  distances  from  the 
sun  are  nearly  equal,  the  moon's  shadow  is  somewhat 
more  than  one  fourth  as  long  as  the  earth's.  Its  length 
varies  because  of  changes  in  the  moon's  distance  from 
the  sun,  caused  chiefly  by  the  varying  distances  of  the 
earth,  which  carries  the  moon  along  with  it.  When  the 
moon  is  between  the  other  two  bodies,  its  shadow  is  at 
times  too  short  to  reach  the  earth  ;  at  other  times  it  is 
long  enough  and  makes  a  small  dark  spot  on  the  earth's 
surface.  Since  the  moon  is  continually  in  motion,  the 
shadow  travels  eastward  over  the  earth  ;  the  earth  is 
turning  in  the  same  direction.  If  the  shadow  is  now 
falling  on  the  city  of  New  York,  there  is  a  race  between 
the  city  and  the  shadow  ;  but  the  latter  is  the  swifter 
and  passes  out  upon  the  Atlantic.  A  shot  from  a  rifled 
gun  would  keep  it  company  for  a  brief  space  of  time.  It 
is  not  often  more  than  150  miles  in  diameter,  and  cuts  a 
pretty  small  swath  on  the  earth's  surface. 

Any  one  who  establishes  himself  within  the  limits  of 
the  swath  may  see  the  sun  totally  eclipsed,  if  the  sky  be 
clear,  during  the  time  occupied  by  the  shadow  in  pass- 
ing over  him.  An  observer  near  the  path  of  the  shadow 
may  see  the  sun  partially  eclipsed.  On  rare  occasions 
there  is  an  interrupted  view  of  the  corona  and  promi- 
nences for  six  or  eight  minutes  before  the  brilliant 
photosphere  peeps  out  at  one  edge  of  the  retreating 
moon,  and  floods  the  landscape  writh  light.  Ordinarily 
the  sun  is  entirely  covered  for  only  two  or  three  minutes. 

A  total  solar  eclipse  is  one  of  the  most  awe-inspiring 
phenomena  of  nature.  The  approach  of  the  moon, 
which  quietly  eats  its  way  into  the  solar  disc,  is  not  no- 


The  Moon  and  Eclipses.  229 

ticed  by  those  who  are  uninformed.  For  .the  sunlight  is 
so  piercing  that  no  special  diminution  of  it  is  perceived  ^otsal  solar 
until  the  eclipse  is  well  advanced.  At  last  the  light  be- 
gins to  pale,  as  though  a  haze  were  forming  over  the  sun. 
One  who  takes  a  quick  upward  glance,  or  employs  a 
dark  glass,  sees  that  the  sun  is  now  a  narrow  cres- 
cent. The  supreme  moment  is  at  hand  ;  the  landscape 
assumes  an  unearthly  hue.  The  beholders  are  silent  and 
stricken  with  awe.  One  stationed  on  a  mountain  may 
see  the  shadow  advancing  over  the  plain  below  with  ap- 
palling speed.  In  but  a  moment  it  has  come  ;  the  moon 
hangs  in  mid-heaven,  a  ball  of  inky  blackness,  fringed 
with  blazing  prominences,  and  enveloped  by  the  silvery 
corona.  The  moments  are  counted  by  heart-beats.  The 
planets  and  brighter  stars  bedeck  the  sky  ;  perchance  a 
stray  comet  peers  forth  in  the  sun's  vicinity.  The  up- 
turned faces  of  the  onlookers  are  ghastly.  A  piercing 
ray  of  light  springs  from  the  edge  of  the  moon  ;  the 
prominences  are  gone.  The  corona  fades  away ;  the 
stars  return.  The  landscape  glows  with  the  returning 
light.  The  sublime  spectacle  is  over. 

It  has  not  been  without  curious  effects  upon  the  lower 

i  c  •  T-I  111'.  Effects  on 

orders  01  creation.      Ine  convolvulus  closes  its  leaves,    plants  and 

...  ,,     .  1-1  animals. 

birds  cease  flying,  chickens  go  to  roost,  beasts  leave 
their  food,  bees  return  to  the  hives,  caged  birds  die  of 
fright  or  thrust  their  heads  under  their  wings,  crickets 
sound  their  nocturnal  notes,  bats  fly  about  ;  some  horses 
seem  to  be  overcome  with  fright  and  sink  down  in  the 
street ;  others  are  blind  to  the  changes  about  them,  and 
go  on  without  even  pricking  up  their  ears.  Oxen  have 
been  known  to  arrange  themselves  in  a  circle,  heads  out- 
ward, as  if  fearing  attack. 

Among  semi-civilized  or  savage  nations  a  solar  eclipse  superstitious 
inspires   great   terror.       Hindus    believe    that   a   great  terron 


230 


A  Study  of  the  Sky. 


Work  during 
an  eclipse. 


Small  planets. 


dragon  is  striving  to  devour  the  sun.  They  fill  the  air 
with  unearthly  screams  and  shouts,  and  beat  their  gongs 
fiercely  ;  the  monster  must  be  frightened  away.  Great 
is  their  joy  when  the  voracious  jaws  eject  the  scorching 
morsel. 

We  have  gone  far  afield,  and  must  return  to  summa- 
rize briefly  some  of  the  work  which  modern  astrono- 
mers attempt  during  the  fleeting  moments  of  a  total 
solar  eclipse. 

I.  The  prominences  and  corona  are  observed  tele- 
scopically. 

II.  Spectroscopic  observations  are   made   of  the  co- 
rona, the  protuberances,  and  the  chromosphere. 

III.  The  light  of  the  corona  is  studied  with  the  polari- 
scope  ;  the  purpose  is  to  determine  the  relation  between 
the  light  which  the  coronal  particles  reflect  and   that 
which  they  emit  because  of  their  incandescence. 

IV.  A  search  for  possible  small  planets  revolving  in 
the  neighborhood  of  the  sun,  and  usually  hidden  by  its 
glare,  is  prosecuted.     Reports  of  the  discovery  of  such 
bodies  have  been  the  subject  of  rather  acrimonious  dis- 
cussion.     Professors  Watson  and  Swift  announced  such 
discoveries  during  the  eclipse  of  July  29,    1878,  but  no 
similar  observations  have  been  made  at  any  succeeding 
eclipse. 

V.  Photographs  of  the  corona  and  of  the  prominences, 
being  more  trustworthy  than  hurried  drawings,  are  much 
in  vogue. 


CHAPTER  XIII. 

MERCURY  AND  VENUS. 

'  Lo  !  in  the  painted  oriel  of  the  West, 
Whose  panes  the  sunken  sun  incarnadines, 
Like  a  fair  lady  at  her  casement,  shines 
The  evening  star,  the  star  of  love  and  rest." 

— Longfellow. 

MERCURY  and  Venus  are  denominated  inferior  plan-  inferior 
ets  because  their  distances  from  the  sun  are  less  than  planets- 
that  of  the  earth. 

They  are  in  conjunction  when  they  appear  to  us  to  be  Con-unction 
nearly  in  line  with  the  sun  ;  the  word  conjunction  sug- 
gests this.  An  inferior  conjunction  of  Mercury  or 
Venus  occurs  when  the  planet  is  between  the  sun  and 
the  earth  ;  a  superior  conjunction  takes  place  when  the 
planet  is  beyond  the  sun.  When  at  inferior  conjunction 
a  planet  may  come  so  near  a  line  joining  the  centers  of 
the  earth  and  sun  that  it  is  seen  against  the  background 
of  the  solar  disc  as  a  small  black  circle  moving  across  its 
face.  It  is  then  in  transit.  After  an  inferior  planet 
passes  inferior  conjunction  it  moves  out  toward  the 
right  as  we  stand  facing  the  sun  ;  it  is  then  west  of  the 
sun,  rising  and  setting  before  the  sun  does  each  day.  In 
Fig.  107  S  is  the  sun  and  E  the  earth,  while  the  circle 
represents  the  orbit  of  Venus.  When  Venus  is  at  C  it 
is  in  inferior  conjunction.  It  then  moves  toward  V,  get- 
ting further  and  further  to  the  right  of  the  sun  each 
week.  When  at  V  it  has  attained  its  greatest  apparent 
distance  west  of  the  sun,  and  is  at  its  greatest  western 

231 


232 


A  Study  of  the  Sky. 


Elongation. 


Morning  and 
evening  star. 


Phases. 


elongation.  When  moving  from  V  toward  C'  it  appar- 
ently approaches  the  sun.  C'  is  the  point  of  superior 
conjunction.  After  passing  C'  Venus  is  at  the  left  of  the 
sun,  rising  and  setting  after  the  sun  does.  V  is  the 
point  of  greatest  eastern  elongation.  After  passing  V 
the  planet  swings  back  toward  the  sun. 

In  this  explanation  we  have  tacitly  assumed  that  the 

earth  is  at  rest  ;  in  reality 
it  is  moving  in  the  same 
direction  as  Venus,  but 
more  slowly.  This  simply 
lengthens  the  time  which 
elapses  between  inferior 
conjunction  and  greatest 
western  elongation,  or  be- 
tween any  two  of  the 
positions  which  we  have 
just  denned. 

Greatest  western  elon- 
gation really  comes  when 
Venus  has  arrived  at  V", 
the  earth  meanwhile  having  moved  on  to  E'.  When  an 
inferior  planet  is  west  of  the  sun  it  is  a  morning  star  ; 
when  east  of  the  sun  it  is  an  evening  star  and  is  to  be 
looked  for  in  the  west. 

Since  Mercury  and  Venus  shine  by  reflecting  the  sun- 
light, and  have  no  intrinsic  radiance,  they  exhibit  phases 
similar  to  those  of  the  moon.  At  inferior  conjunction 
the  dark  side  of  the  planet  is  toward  us  ;  as  the  planet 
moves  out  toward  western  elongation  its  phase  is  a  cres- 
cent like  that  of  the  young  moon. 

At  greatest  elongation  the  phase  is  a  semicircle,  like 
the  moon  at  one  of  its  quarters.  When  the  planet  is  at 
superior  conjunction  we  look  full  in  its  illuminated  face, 


FIG.  107.— CONJUNCTION  AND  ELON- 
GATION. 


Mercury  and    Venus.  233 

which  is  a  complete  circle.  Afterward  it  descends 
through  the  gibbous  phase,  to  a  semicircle,  and  thence 
to  a  narrow  crescent  again,  as  it  approaches  inferior 
conjunction. 

Of  Mercury  little  is  known,  for  it  is  coy  and  keeps  M 
close  to  the  sun.  The  most  favorable  times  for  seeing  it 
in  the  evening  are  those  when  it  reaches  its  greatest 
eastern  elongation  in  March  or  April.  For  it  is  then 
nearly  above  the  sun  at  sunset  ;  at  such  a  time  it  may  be 
seen  every  night  for  two  successive  weeks,  one  of  which 
immediately  precedes  the  time  of  elongation.  It  is  then 
very  plain,  even  in  strong  twilight,  and  is  not  likely  to 
be  confounded  with  any  fixed  star. 

Its  mean  distance  from  the  sun  is  36,000,000  miles.    its  distance. 
Its  orbit  is  more  eccentric  than  that  of  any  other  of  the 
large  planets,  so  that  its  actual  distance  from  the  sun 
ranges  from  28,500,000  to  43,500,000  miles. 

Sunlight  upon  Mercury  is  more  than  twice  as  intense  Intensit  of 
when  it  is  nearest  the  sun  as  when  it  is  farthest  away.    sunlight. 
The  average  intensity  is  seven  times  that  which  we  ex- 
perience.    The  diameter  of  the  planet  is  3,000  miles, 
and  eighty-eight  days  are  consumed  in  making  a  revo- 
lution about  the  sun. 

It  is  very  difficult  to  make  out  any  markings  on  Mer-  Rotati 
cury's  disc.  The  Italian  astronomer,  Schiaparelli,* 
whose  observations  of  the  canals  of  Mars  have  proven 
that  he  is  exceptionally  keen  of  sight,  has  observed  cer- 
tain dim  and  ill-defined  spots  whose  motion  renders  it 
probable  that  Mercury  rotates  on  its  axis  in  eighty-eight 
days,  and  thus  presents  the  same  face  continually  to  the 
sun. 

There  is  great  uncertainty  about  the  presence  of  air  or  Air,  water, 
water  ;  certain  spectroscopic  observations  indicate  that  a 

*  Astronomer  at  Milan,  Italy. 


234 


A  Study  of  the  Sky. 


Venus. 


Revolution 
And  rotation. 


Shadings. 


Ice  and  snow. 


there  may  be  a  thin  atmosphere,  in  which  water  vapor 
is  present.  If  these  be  accepted  as  correct,  the  dim 
shadings  described  by  Schiaparelli  may  be  the  outlines  of 
seas  or  continents. 

One  imaginative  astronomer  discovered  mountains  on 
the  planet  about  a  century  ago.  Though  his  telescope 
was  a  pigmy  compared  with  those  of  to-day,  modern 
observers  have  not  verified  the  existence  of  the  moun- 
tains. 

VENUS. 

Venus  is  a  more  interesting  object  than  Mercury  be- 
cause it  comes  nearer  to  us  and  is  larger  and  brighter, 
giving  more  light  than  any  other  planet.  Its  distance 
from  the  sun  is  67,000,000  miles,  and  its  orbit  is  nearly 
a  circle.  It  is  almost  as  large  as  the  earth,  having  a 
diameter  of  7,700  miles. 

Two  hundred  and  twenty-five  days  are  consumed  in 
making  a  revolution  about  the  sun.  The  time  of  rota- 
tion is  generally  given  as  about  twenty-four  hours,  this 
period  having  been  derived  from  old  observations, 
which  have  received  some  confirmation  in  recent  times. 
Schiaparelli' s  investigations  cast  discredit  upon  this 
value,  and  tend  to  show  that  Venus,  like  Mercury, 
keeps  the  same  face  toward  the  sun. 

Many  astronomers  have  seen  shadings  upon  the 
planet's  surface,  but  they  are  so  ill  defined  that  their 
cause  is  unknown.  When  the  planet  is  a  crescent,  the 
horns  are  brighter  than  the  rest  of  the  surface.  Possi- 
bly ice  and  snow  at  the  planet's  poles  cause  this  appear- 
ance. On  the  whole,  it  may  be  said  that  telescopic 
scrutiny  of  Venus  has  decided  nothing  as  to  the  con- 
figuration of  its  surface. 

It  seems  to  be  covered  with  a  dense  atmosphere, 
which  is  an  effectual  bar  to  our  curiosity.  The  existence 


Mercury  and   Venus. 


235 


of  the  atmosphere  is  shown  at  the  times  of  its  transits. 
When  Venus  is  just  about  to  enter  upon  the  sun's  disc,  Atmosphere, 
or  has  just  passed  off,  it  is  surrounded  by  a  tiny  rim  of 
light.  The  sunlight  has 
pierced  through  the  planet's 
atmosphere  and  come  on  to  our 
eyes.  It  is  probable  that  the 
atmosphere  is  denser  than  our 
own,  but  not  more  than  twice 
as  dense.  The  spectrum  con- 
tains lines  which  indicate  the 
presence  of  water  vapor.  It  is 
a  reasonable  inference  that 
Venus  is  a  planet  whose  sky  is 
almost  totally  cloudy,  and 
whose  atmosphere  is  continu- 
ally laden  with  moisture.  On 

a  day  when  the  entire  earth  is  enveloped  in  a  cloud- 
shell,  to  an  inhabitant  of  the  moon  it  would  present,  on 
a  huge  scale,  the  appearance  of  Venus. 


FIG.  108.— MARKINGS  ON 
VENUS. 


CHAPTER  XIV. 

MARS    AND    THE    ASTEROIDS. 

"  And  earnest  thoughts  within  me  rise, 
When  I  behold  afar, 
Suspended  in  the  evening  skies, 
The  shield  of  that  red  star. ' ' 

— Longfellow. 

MARS  is  perhaps  the  most  interesting  planet,  because 
of  the  tantakzing  chase  on  which  he  has  led  observers. 
He  is  at  times  almost  as  near  as  Venus  when  the  latter 
is  in  inferior  conjunction  ;  yet  he  is  even  then  so  far 
away  that  the  more  delicate  features  of  his  surface,  like 

the  canals,  are  seen 
with  great  difficulty, 
and  are  the  source 
of  much  perplexity. 
Even  the  marked 
features  which  have 
for  generations 
passed  unchal- 
lenged under  the 
names  of  continents 
and  seas  are  now 
subjected  to  rigid 
scrutiny,  and  in 

FIG.  109.— MARS.  some    quarters    are 

denied  their  time-honored  appellations.  While  there  is 
a  fair  consensus  of  opinion  as  to  the  majority  of  appear- 
ances seen  upon  the  planet,  there  is  considerable  diver- 

236 


Mars  and  the  Asteroids.  237 

sity  in  the  interpretations  which  are  put  upon  them. 

In  considering  such  a  subject  one  must  maintain  a 
judicial  frame  of  mind,  realizing  that  while  conservatism  mmd.lcu 
is  generally  to  be  preferred  to  rashness,  yet  the  age  of  a 
theory  should  not  shield  it  from  searching  examination, 
as  the  novelty  of  a  result  should  not  debar  it  from  the 
most  candid  treatment. 

The  mean  distance  of  Mars  from  the  sun  is  141,500,- 
ooo  miles.  His  orbit  departs  farther  from  the  circular 
form  than  that  of  any  other  planet  save  Mercury.  The 
difference  between  his  greatest  and  least  distances 
from  the  sun  is  26,000,000  miles.  He  is  best  seen 
when  the  earth  lies  between  him  and  the  sun  ;  we  are 
then  nearer  to  him  than  at  other  times,  and  he  appears 
bigger  and  brighter. 

At  such  a  time  if  he  happens  to  be  near  perihelion, 

.  .    ,     .       ,  .     ,  .  .     .         Perihelion  and 

which  is  the  point  of  closest  approach  to  the  sun,  and  the  aphelion, 
earth  is  near  its  aphelion,  which  is  the  point  of  furthest 
recession  from  the  sun,  the  distance  between  the  two 
bodies  is  but  36,000,000  miles.  This  close  approach 
occurs  every  fifteen  years,  and  took  place  in  August, 
1892,  for  the  last  time  during  the  nineteenth  century. 

All  those  planets  whose  orbits  are  larger  than  that  of 
the  earth  are  called  superior  planets.  When  the  earth  is  pSSSs!r 
nearly  in  a  line  between  a  superior  planet  and  the  sun, 
so  that  the  former  appears  to  be  on  the  opposite  side  of 
the  celestial  sphere  from  the  sun,  it  is  said  to  be  at 
opposition.  When  the  planet  is  beyond  the  sun  and 
nearly  in  line  with  it,  it  is  in  conjunction.  When  Mars 
is  at  a  favorable  opposition  it  is  more  than  fifty  times  as 
bright  as  at  conjunction,  and  rivals  Jupiter  in  splendor. 
When  far  from  opposition  it  might  readily  be  mistaken 
for  a  red  fixed  star,  did  not  its  motion  betray  its  true 
character. 


238 


A  Study  of  the  Sky. 


and 


rotation. 


The  moons. 


The  diameter  of  Mars  is  4,  200  miles.  It  consumes 
687  days,  or  nearly  twenty-three  months,  in  making  one 
revolution  about  the  sun.  Some  of  the  .markings  on  its 

surface  are  so  well 
defined  and  stable 
that  the  time  of  ro- 
tation has  been 
found  very  accu- 
rately by  comparing 
drawings  made  in 
the  seventeenth  cen- 
tury with  modern 
ones.  The  received 
value  is  24hr-  37min- 
22.67sec-  The  ro- 
tation axis  of  the 

FIG.  IIO.-PROJECTIONS  ON  THE  POLAR  CAP.      planet  is  not  perpen- 

dicular to  the  plane  of  its  orbit,  but  deviates  27°  from 
that  position.  Therefore  there  must  be  seasonal  changes 
on  Mars  just  as  on  the  earth. 

Two  tiny  moons  attend  the  planet  ;  they  were  discov- 
ered at  the  favorable  opposition  of  1877  by  Professor 
Asaph  Hall.*  Their  names,  Deimos  and  Phobos,  are 
translations  of  Greek  words  used  by  Homer  as  designa- 
tions of  the  fiery  steeds  which  drew  the  chariot  of 
the  god  of  war.  They  are  the  smallest  known  bodies  in 
the  solar  system,  with  the  exception  of  meteors.  Dei- 
mos occupies  3ohrs-  i8min-  in  making  one  revolution,  and 
is  12,500  miles  from  the  planet's  surface.  From  meas- 
ures of  its  brightness  its  diameter  has  been  estimated  at 
five  or  six  miles.  Phobos,  the  inner  moon,  is  only  3,700 
miles  from  the  surface  of  Mars  ;  it  accomplishes  a  revo- 


*  Then  an  astronomer  at  the  United  States  Naval  Observatory  at  Washing- 
ton ;  now  on  the  retired  list. 


Mars  and  the  Asteroids. 


239 


lution    in  7hr-  39  min-  and  is  the  only  known  moon  which 

makes  the  trip  around  its  primary  in  less  time  than  the  A  ^uick  triP- 

primary  takes  to  turn  once  on  its  axis.     In  consequence 

of  this  unusual  speed  it  rises  in  the  west  and  sets  in 

the  east.     A  man  living  near  one  of  the  poles  of  Mars 

would  never  see  Phobos,  because  it  revolves  in  the  plane 

of  the  Martian  equator,  and  keeps  close  to  the  planet. 

To  us  they  seem  to  fill  the  office  of  nocturnal  luminaries 

very  imperfectly,  the  light  given  by  Phobos  to  possible 

Martians  being  but  one  sixtieth  of  our  moonlight.    Dei- 

mos    sheds    upon 

Mars     only     one 

twentieth   as    much 

light   as    Phobos. 

They    go    through 

the  same  phases  as 

our  own  moon.* 

The  planet  itself 
is  subject  to  changes 
of  phase.  At  op- 
position, when  the 
earth  is  between  the 
sun  and  Mars,  the 
latter  exhibits  a  full, 


FIG.  in. — THE  LAKE  OF  THE  SUN. 


round   disc,    as   we 
are  directly  in  front  of  its  illuminated  hemisphere  ;  at  Phases  of  the 
conjunction  it  has  the  same  phase,  but  at  intermediate  Planet- 
times  we  cannot  see  all  of  the  bright  hemisphere. 


*  The  discovery  of  these  satellites  was  curiously  anticipated  by  Kepler, 
Dean  Swift,  and  Voltaire.  One  of  Kepler's  strange  speculations,  which  he 
mentioned  in  a  letter  to  Galileo,  was  that  Mars  had  two  moons,  Saturn  six  or 
eight,  while  Mercury  and  Venus  were  possibly  blessed  by  a  single  attendant 
each.  Dean  Swift  represents  in  "  Gulliver's  Travels  "  that  the  scientific  Lilli- 
putians had  telescopes  of  great  power,  with  which  they  had  discovered  "two 
lesser  stars  or  satellites  which  revolve  about  Mars."  Voltaire  makes  a  hypo- 
thetical inhabitant  of  Sirius  take  a  celestial  voyage,  in  the  course  of  which  he 
visits  Mars  and  sees  two  moons  which  are  intended  to  make  up  for  the  compara- 
tive feebleness  of  the  sunlight. 


240 


A  Study  of  the  Sky. 


The  polar  caps. 


The  general 
surface. 


The  canals. 


The  most  conspicuous  appearances  on  the  face  of 
Mars  are  roundish  white  masses  at  the  poles.  They  were 
plainly  seen  soon  after  the  invention  of  the  telescope, 
and  have  been  observed  ever  since.  Neither  one  of 
them  maintains  a  uniform  size.  When  summer  reigns 
in  the  northern  hemisphere  of  the  planet  the  white  area 
around  the  north  pole  diminishes  and  almost  vanishes  ; 
when  summer  yields  to  winter  the  white  spot  grows 
again.  In  October,  1894,  the  south  polar  spot  became 
so  small  that  many  astronomers  believed  that  it  had  van- 
ished. But  the  Lick  telescope,  under  the  manipulation 
of  Professor  E.  E.  Barnard,  still  showed  it,  though  with 
great  difficulty  ;  it  was  very  small,  and  seemed  to  be 
partially  obscured  by  an  overhanging  veil.  The  polar 
caps  are  supposed  to  be  composed  of  snow  and  ice. 

Most  of  the  planet's  surface  is  of  a  yellowish-red 
color  ;  the  remainder  is  usually  of  a  dark  gray  tint. 
Many  maps  have  been  made,  which  agree  quite  satis- 
factorily in  their  main  details.  The  yellowish-red  re- 
gions are  thought  to  be  dry  land  ;  the  dark  gray  regions 
bodies  of  water. 

Fig.  112  exhibits  several  of  the  canals.  Schiaparelli 
was  not  the  first  astronomer  to  notice  them  :  some 
were  observed  by  several  distinguished  astronomers  be- 
fore his  day.  But  he  has  found  so  many  that  they  are 
by  common  consent  called  ' '  Schiaparelli' s  canals. ' '  No 
other  observer,  however  large  his  instrument,  has  com- 
pletely verified  the  mysterious  network  with  which 
Schiaparelli' s  map  is  covered.*  The  majority  of  the 
canals  are  several  hundred  miles  long.  A  canal  occa- 
sionally appears  to  be  doubled  ;  that  is,  a  new  canal 


*  However,  Mr.  Percival  Lowell,  and  the  observers  associated  with  him,  at 
Flagstaff,  Arizona,  have  mapped  a  large  number  of  canals  not  detected  by 
Schiaparelli.  An  account  of  these  is  given  in  Mr.  Lowell's  book  entitled 
"  Mars." 


Mars  and  the  Asteroids. 


241 


appears  running  by  the  side  of  the  old  one.  Schia- 
parelli  states  that  this  duplication  is  probably  periodi- 
cal,  and  has  some  connection  with  the  changes  of  the 
seasons.  Several  canals  often  meet  at  a  point,  as 
though  they  were  spokes  radiating  from  a  hub.  They 
are  the  most  mysterious  objects  on  Mars,  and  a  host  of 
theories  have  been  broached  about  them.  Schiaparelli 
has  suggested  that  they  may  be  natural  water-ways 


FIG.  112. — CANALS. 

through  which  the  waters  caused  by  the  melting  of  the 
polar  snows  flow  toward  the  equator. 

There  are  other  more  transient  appearances.  Some- 
times there  are  small  spots  of  tolerably  definite  outline 
which  are  visible  for  a  time  and  then  vanish.  At  other 
times  there  are  large  diffuse  patches,  which  seem  to 
obscure  the  familiar  outlines  shown  on  the  map.  Both 
of  these  appearances  may  be  ascribed  to  clouds.  Large 
reddish  areas  now  and  then  have  a  whitish  aspect,  as 
though  snow  had  fallen  upon  them.  One  small  orange 
spot  has  often  appeared  white  :  perhaps  it  is  a  moun- 


of 


Clouds  and 
snow. 


242 


A  Study  of  the  Sky. 


Inundations. 


Melting  of 
a  cap. 


tain  or  high  table-land,  where  snow  falls  readily.  Pro- 
jections like  saw-teeth  are  seen  on  the  edge  of  the  disc. 
Some  of  these  may  be  large  clouds  floating  high  in  the 
atmosphere  of  Mars  ;  others  may  be  due  to  mountains. 
Large  dark  regions  extend  their  boundaries,  and 
seem  to  obliterate  adjoining  yellowish  ones.  After 
several  weeks  or  months  they  resume  their  usual  form. 


FIG.  113. — PROJECTIONS  ON  THE  EDGE  OF  THE  Disc. 

If  lowlands  adjoin  a  sea,  their  inundation  would  cause 
such  changes  of  appearance. 

When  a  polar  cap  is  diminishing,  a  dark  rim  has 
been  seen  about  it,  as  if  it  were  bordered  by  the  water 
coming  from  the  melting  cap.  In  1892  the  south  polar 
cap  dwindled  very  rapidly,  and  there  were  very  inter- 
esting changes  in  its  vicinity.  It  lost  1,500,000  square 
miles  of  its  area  in  a  month.  At  first  a  dark  spot 


Mars  and  the  Asteroids. 


243 


appeared  in  the  midst  of  the  cap  ;  it  gradually  enlarged 
and  cleft  the  cap  in  twain.  A  part  of  the  region  be-  An  overflow, 
tween  the  diminished  cap  and  one  of  the  well-known 
dark  portions  of  the  disc  became  dark,  and  then  the 
dark  region  just  mentioned  was  enlarged,  intrenching 
upon  the  adjacent  lighter  regions.  All  of  this  is  readily 
explained  on  the  assumption  that  the  first  dark  spot 
within  the  polar  cap  was  water,  which  had  been  pro- 
duced by  the  melting  of  the  snow  and  ice.  If  this  snow- 
water found  its  way  across  lowlands  to  an  adjacent 
sea,  and  caused  the  latter  to  overflow  its  boundaries, 
the  phenomena  which  followed  the  melting  of  the  polar 
cap  in  1892  are  explained. 

There  is  one  dark  spot  called  Lacus  Solis,  the  Lake  LacusSoiis. 
of  the  Sun,  which  is 
plain  at   every   op- 
position.    It  is  sur- 
rounded by  a  bright 
ring,  which,  accord- 
ing to  our  previous 
theorizing,    is    dry 
land.       Sometimes 
the  ring  is  wide  and 
conspicuous  ;    at 
others   it  is  narrow 
and  not  easily  seen. 
A  large  dark  spot, 
thought    to    be   an 
ocean,    is   near   at 
hand  ;  at  times  canals  connect  the  lake  with  the  ocean, 
traversing  a  portion  of  the  bright  ring  ;  at  other  times 
there  is  a  break  in  the  bright  ring,  which  then  looks 
like  a  horse-shoe,  the  vanished  portion  of  the  original  A  horse-shoe- 
bright  ring  being  dark  ;   the  lake  and  the  sea  are  ap- 


FIG.  114.— CANALS  CONNECTED  WITH  LACUS 
SOLIS. 


244 


A  Study  of  the  Sky. 


The  canals  fill. 


Various 
theories. 


Irrigation. 


parently  joined.  If  the  land  separating  the  lake  from 
the  sea  is  low,  and  slight  changes  in  the  water  level 
are  admitted,  the  preceding  changes  in  appearance  may 
be  explained.  When  the  water  is  low  the  bright  ring  is 
complete  ;  when  it  is  a  little  higher  it  fills  the  canals  ; 
when  it  is  still  higher  it  inundates  the  portion  of  the 
bright  ring  lying  between  the  two  bodies  of  water. 


FIG.  115.— THE  POLAR  CAP  IN  JULY  AND  AUGUST,  1892. 

Plausible  as  all  the  theories  about  snow,  seas,  dry 
land,  clouds,  and  inundations,  which  have  been  ad- 
vanced, may  appear,  we  must  not  forget  that  they  are 
all  subject  to  revision  when  new  light  is  obtained.  The 
most  variant  theories  have  already  been  proposed.  It 
has  been  suggested  that  the  polar  caps  are  simply 
masses  of  cloud  ;  that  the  bright  portions  of  the  planet's 
surface  may  be  water,  while  the  dark  ones  are  land  ; 
that  the  doubling  of  the  canals  is  an  illusion  ;  that  the 
canals  are  not  to  be  considered  as  water-ways,  but  as 
streaks  of  vegetation  bordering  upon  streams  which  are 
themselves  too  narrow  to  be  seen.  One  writer  says 
that  the  canals  are  so  straight  and  so  well  distributed 
over  the  planet's  surface  that  they  may  be  considered 
as  the  work  of  intelligent  beings,  who  use  them  for 
purposes  of  irrigation.  Another  remarks  that  they  are 
indefinite  shadings,  vague  in  outline,  and  often  discon- 
tinuous. 

The  popular  interest  in  Mars  has  arisen  largely  from 


Mars  and  the  Asteroids. 


245 


the  possibility  that  it    is    habitable    by    human  beings. 

Practical  astronomers  generally  look  upon  such  specula-   Habitabiiity. 

tions  with  ill-disguised  disdain  ;  let  us  examine  into  the 

matter  for  a  moment.      If  there  be  land  and  water,   and 

freedom  from  disastrous  inundations,  in  certain  regions, 

a  man  would  simply  need  an  atmosphere  like  our  own, 

and  a  suitable  supply  of  warmth,  together  with  a  fertile 

soil. 

What  has  been  determined  concerning  the  atmos-  Theatmos. 
phere  ?  If  it  were  as  dense  as  our  own,  and  of  similar  Phere- 
composition,  we  could  not  see  the  polar  caps  and  other 
prominent  features  so  distinctly.  The  color  of  the  caps 
would  be  altered  from  white  to  a  reddish  tint,  since  we 
always  see  them  obliquely  through  quite  a  thickness  of 
atmosphere.  Furthermore  the  spectrum  of  Mars  should 
contain  strong  absorption  bands  if  the  atmosphere  were 
dense.  More  than  one  European  astronomer,  using  a 
comparatively  small  instrument,  has  found  spectroscopic 
evidence  of  the  existence  of  water  vapor  in  the  planet's 


FIG.  116. — CANALS  IN  AUGUST,  1892. 

atmosphere.  But  Professor  Campbell,*  with  a  large 
spectroscope  attached  to  the  great  Lick  telescope,  found 
no  evidence  of  water  vapor,  and  sees  no  absorption 
bands  whatever.  In  his  opinion  such  bands  would  have 
been  evident  if  the  atmosphere  of  Mars  were  one  fourth 

,  .  .  ,     A  man  would 

as  dense  as  our  own.     A  man  therefore  would  gasp  and  gasp  and  die. 

*  Of  the  Lick  Observatory. 


246  A  Study  of  the  Sky. 

die,   if  Professor  Campbell's  conclusions  are  to  be  ac- 
cepted. 

A  warm  cii-  ^he  cnmate  of  tne  planet  seems  to  be  mild  ;  else  why 

mate.  should  the  polar  snows  melt  so  rapidly  and  cause  fresh- 

ets ?     The  sunlight  which  reaches  Mars  is  less  than  half 
as  intense  as  ours. 

If  its  atmosphere  be  rare,  why  has  it  such  a  power  of 

Composition  of     .  ,  «  . 

the  atmosphere,  imprisoning  the  sunbeams  and  keeping  the  planet  warm  ? 
Are  we  not  led  by  this  course  of  reasoning  to  suspect 


FIG.  117.— THE  CAP  DIMINISHING,  AUGUST  24-29,  1892. 

that  the  composition  of  the  Martian  atmosphere  is  widely 
different  from  that  of  our  air  ?  Would  not  a  human 
being  fare  ill  on  Mars  ? 

Caution  While  the  basis  of  our  argument  is   confessedly  slen- 

der, and  the  conclusions  may  be  wide  of  the  facts,  does 
not  the  best  light  available  indicate  that  Mars  is  prob- 
ably not  a  suitable  place  for  human  habitation?  We 
cannot  deny  that  our  neighbor  may  be  inhabited ;  its  in- 
habitants may  be  far  superior  to  mankind,  in  both  phys- 
ical and  mental  endowments.  But  such  speculations  are 
no  part  of  the  science  of  astronomy. 

THE    ASTEROIDS. 

An  arithmetical       ^n  t^ie  ^car  :7?2  Pro^essor  Johann  Titius,  of  Witten- 

scheme.  berg,  devised  an  arithmetical  scheme  for  representing 

the  relative  distances  of  the  planets  from  the  sun.     By 

adding  four  to  each  of  the  numbers  o,  3,  6,    12,  24,  48, 


Mars  and  the  Asteroids.  247 

and  96,  he  obtained  a  series  which  approximately  repre- 
sented the  data.  If  we  represent  the  earth's  distance 
by  10,  the  correspondence  between  theory  and  fact  is 
shown  below  : 

Theory.  Fact. 

Mercury  J '„• 4  3.9 

Venus 7  7.2 

Earth 10  10.0 

Mars 16  15.2 

Jupiter 52  52.0 

Saturn.   .,.-.. 100  95.4 

The  gap  between  Mars  and  Jupiter  made  a  profound  The  gap. 
impression  upon  Bode,  a  Berlin  astronomer,  and  he 
boldly  predicted  that  a  planet  would  some  day  be  found 
which  would  fill  out  the  series.  The  discovery  .  of 
Uranus  in  1781  at  a  distance  agreeing  fairly  with  the 
next  term  of  the  series  gave  a  powerful  impetus  to  the 
idea  that  there  must  be  a  planet  between  Mars  and 
Jupiter. 

Half  a  dozen  German  astronomers  formed  an  associa-   Celestial  police, 
tion  of  celestial  police  to  search   for  the  truant  planet. 
Before  these  officers  had  gotten  their  belts  fairly  tight- 
ened up,  a  Sicilian  astronomer,  Piazzi  by   name,   caught 
sight  of  the  missing  body. 

He  was  engaged  in  the  somewhat  prosaic  work  of  The  discovery, 
making  a  star  catalogue,  and  had  observed  the  right 
ascensions  and  declinations  of  a  large  number  of  stars. 
On  January  i,  1801,  the  first  evening  of  the  century,  he 
observed  the  position  of  a  star  of  the  eighth  magnitude  ; 
on  the  next  night  he  observed  it  again.  The  two  obser- 
vations did  not  agree.  The  third  night  he  tried  it,  and 
encountered  another  disagreement.  He  was  satisfied 
that  it  was  in  motion,  and  observed  it  for  six  weeks, 
until  a  serious  illness  seized  him. 

Meanwhile  he  had  written  letters  to  Bode  and  another 


248 


A  Study  of  the  Sky. 


Gauss. 


astronomer,  telling  of  his  good  fortune  ;  but  there  were 
Delayed  letters.  no  express  trains  in  those  days,  and  the  letters  tumbled 
about  for  a  couple  of  months  before  they  reached  their 
destinations.  It  was  then  too  late  to  look  for  the  new 
body,  for  the  sun  had  gotten  around  into  that  part  of 
the  sky.  The  celestial  police  took  extra  hitches  in  their 
belts  and  ruminated,  but  their  ruminations  were  of  no 
avail ;  not  one  of  them  could  find  out  where  to  look  for 
the  fugitive,  after  the  sun  had  passed  by. 

A  rising  young  mathematician,  Gauss  by  name,  who 
afterward  became  one  of  the  foremost  of  astronomers, 
set  himself  at  work  on  the  problem  and  unraveled  the 
hard  knots  in  it.  By  November  he  was  able  to  tell  the 
celestial  police  (as  they  called  themselves)  where  to 
hunt.  The  clouds  and  storms  of  winter  now  baffled  the 
searchers.  But  on  the  last  day  of  the  year  the  fugitive 
was  caught.  AtPiazzi's  request  it  was  named  after  one 
of  the  lesser  divinities,  Ceres,  the  tutelary  goddess  of 
Sicily. 

Three  months  afterward  Olbers,  of  Bremen,  chanced 
other  asteroids,  upon  a  similar  object,  which  proved  to  be  another  small 
planet,  revolving  in  an  orbit  of  nearly  the  same  size  as 
that  of  Ceres.  To  it  the  name  Pallas  was  given. 
Within  half  a  dozen  years  two  more,  Juno  and  Vesta, 
were  captured.  The  progress  of  discovery  was  slow  up 
to  1850,  when  about  thirteen  were  known. 

The  method  of  search  was  laborious,  but  easily  under- 
stood. Star  charts  were  constructed,  showing  all  stars 
(except  the  very  minutest)  visible  in  certain  regions  of 
the  sky.  Night  after  night  the  charts  were  compared 
with  the  heavens  to  see  if  any  object  not  on  the  chart 
was  in  evidence.  Whenever  a  faint  star-like  object  was 
found  to  be  in  motion,  it  was  hailed  as  a  new  minor 
planet,  observed  with  diligence,  enchained  by  the  toils 


The  old  method 
of  search. 


Mars  and  the  Asteroids.  249 

of  mathematics,  and  finally  imprisoned  in  an  astronomi- 
cal almanac. 

Nowadays  astronomers  hunt  this  sort  of  game  with  a   The  new 
camera,  which  is  attached  to  a  telescope  of  short  focal  method- 
length,  having  a  large  field  of  view.     The  image  of  each 
star  photographed  is  a  tiny  point  on  the  sensitive  plate. 
The  photographic  signature  of  an  asteroid  differs  from 


FIG.  118. — ASTEROID  TRAIL  ON  A  PHOTOGRAPH  OF  THE  PLEIADES. 

that  of  a  star ;  since  it  is  in  motion  with  reference  to  the 
surrounding  stars,  its  image  on  the  plate  moves,  produ- 
cing a  short  streak.  When  the  plate  is  developed  the 
astronomer  soon  discovers  this  anomalous  mark  among 
the  other  little  dots,  and  knows  that  he  has  photographed 
an  asteroid,  new  or  old. 

A  "Rechen  Institut"  in  Berlin,  composed  of  astro-   who  takes 
nomical  computers,  takes  care  of  these  members  of  the   careofthem? 


250 


A  Study  of  the  Sky. 


Their  orbits. 


Their  sizes. 


sun's  family,  sifts  out  the  new  ones  from  those  previously 
known,  computes  their  orbits,  predicts  their  places 
from  year  to  year,  and  calls  attention  to  those  whose 
orbits  are  not  yet  securely  determined,  so  that  they 
may  be  observed  afresh  before  they  are  lost.  They  now 
(1896)  number  over  400,  and  are  being  discovered  too 
rapidly  for  the  comfort  of  the  computers  who  have  them 
in  charge.  By  the  end  of  the  nineteenth  century  five  or 
six  hundred  of  them  will  probably  be  known  unless  the 
zeal  of  certain  astronomical  photographers  is  checked. 

The  mean  distances  of  the  known  asteroids  range  from 
200,000,000  to  400,000,000  miles,  and  their  periods  of 
revolution  from  three  to  nine  years.  A  few  of  them  ap- 
proach so  near  Jupiter  as  to  suffer  considerable  perturba- 
tions by  their  giant  brother.  One  of  them  is  sometimes 
nearer  the  sun  than  is  Mars.  Despite  the  great  entan- 
glement of  the  various  orbits,  there  is  no  special  danger 
of  collision,  except  on  the  part  of  Fides  and  Maia,  which 
may  become  united  into  one  body  or  become  a  system 
like  the  earth  and  moon. 

Vesta  is  the  brightest  and  is  occasionally  visible  to  the 
naked  eye.  The  diameters  of  four  of  them  have  been 
measured  by  Professor  Barnard  with  the  Lick  telescope 
with  the  following  results  : 

Ceres \ 485  miles. 

Pallas 304  miles. 

Juno 118  miles. 

Vesta 243  miles. 

Their  faintness  indicates  that  most  of  them  do  not  ex- 
ceed fifty  miles  in  diameter.  Those  which  are  discov- 
ered by  photography  are,  as  a  rule,  decidedly  insignifi- 
cant, many  of  them  having  probably  as  small  a  diameter 
as  ten  miles.  Five  hundred  of  them  together  would  be 
only  a  millionth  as  large  as  the  earth. 


Mars  and  the  Asteroids.  251 


A  man  would  be  much  interested  in  paying  a  visit  to 
one  of  these  tiny  worlds,  if  he  could  get  along  without  Asteroid0  an 
his  usual  supply  of  air,  and  endure  the  rigors  of  cold 
which  obtain  there.  If  the  asteroid  were  composed  of 
as  dense  materials  as  the  earth,  and  were  only  eight 
miles  in  diameter,  the  force  of  gravity  at  its  surface 
would  be  one  thousandth  as  great  as  on  the  earth.  A 
baby  who  tosses  a  ball  to  a  height  of  five  feet  could  there 
toss  the  same  ball  a  mile.  The  man  could  throw  a  base- 
ball clear  off  the  planet.  Should  he  essay  to  walk,  the 
first  spring  of  his  ankle  would  project  him  upward  off 
the  ground.  An  attempt  at  running  would  be  a  ludi- 
crous series  of  one-legged  leaps.  Should  he  leap  off  a 
cliff  1,000  feet  high,  he  would  reach  the  bottom  in  a  lit- 
tle over  four  minutes,  and  would  experience  no  more 
severe  a  shock  than  if  he  had  jumped  down  a  space  of 
one  foot  on  the  earth.  If  he  tried  to  sit  down,  his  feet 
would  be  lifted  off  the  ground,  and  he  would  gently  fall 
into  his  seat.  If  he  lifted  up  a  basket  of  eggs  with  no 
more  care  than  he  would  take  on  the  earth,  the  eggs 
would  leave  the  basket,  rise  about  140  feet,  and  return 
in  three  minutes  and  a  fraction.* 

At  first  it  was  supposed  that  the  asteroids  were  frag-  Origin  of the 
ments  of  a  larger  planet,  which  had  been  shattered  by  asteroids, 
an  explosion.  If  this  were  the  case,  the  orbits  of  all  the 
fragments  would  at  first  intersect  at  the  point  where  the 
explosion  occurred.  The  disturbances  caused  by  the 
attractions  of  the  other  planets  would  so  alter  the  differ- 
ent orbits  that  after  a  few  thousand  years  they  would 
be  very  far  from  meeting  at  any  given  point.  The 
changes  which  a  few  of  the  orbits  have  undergone  in  the 
past  have  been  approximately  ascertained,  and  no  clue 
to  a  common  point  of  intersection  has  been  found.  The 

*  These  calculations  are  based  on  an  initial  velocity  of  three  feet  a  second. 


252  A  Study  of  the  Sky. 

hypothetical  explosion  must  have  occurred  hundreds  of 
thousands  or  millions  of  years  ago,  if  ever. 

According  to  the  nebular  hypothesis  (to  be  set  forth 

matter  °f  hereafter),  the  asteroids  may  have  arisen  from  the  con- 

.   densation  of  a  ring  of  nebulous  matter,  which  was  left 

behind,  as  the  original  solar  nebula  contracted.     This  is 

the  commonly  received  explanation  of  their  origin. 


CHAPTER    XV. 

JUPITER,    SATURN,    URANUS,    AND    NEPTUNE. 

"  Some  displaying 

Enormous  liquid  plains,  and  some  begirt 
With  luminous  belts,  and  floating  moons,  which  took, 
Like  them,  the  features  of  fair  earth." 

— Byron. 

JUPITER  is  the  giant  of  the  sun's  family  of  planets. 
The  distance  from  pole  to  pole  is  over  84,000  miles.  At  dimensions 
the  equator  his  diameter  is  nearly  90,000  miles.  He  is 
therefore  decidedly  out  of  round.  The  elliptical  shape 
of  his  disc  is  readily  perceived  with  a  telescope,  or  in 
any  good  picture  of  him.  So  marked  an  equatorial 
bulge  may  be  due  to  one  or  both  of  two  causes.  He 
may  rotate  with  extreme  rapidity,  so  that  the  ' '  centrif- 
ugal force  ' '  at  the  equator  is  large,  or  he  may  be  so 
plastic  that  even  a  low  velocity  of  rotation  would  cause 
the  bulging  observed.  As  we  shall  see  presently,  there 
is  good  reason  to  believe  that  both  of  these  causes 
operate. 

His  bulk  is    1,300  times  that  of  the  earth  ;    all  the 

Size,  distance, 

other  planets  compacted   together  into  one  would  not  and  time  of 

.      .  revolution. 

equal  him  in  volume.  His  mean  distance  from  the  sun 
is  483,000,000  miles,  which  is  more  than  five  times  the 
earth's;  n.86  years  are  occupied  in  one  revolution 
about  the  sun. 

Like  all  other  superior  planets  he  is  brightest  at  Hisa 
opposition,  attaining  then  a  luster  which  exceeds  that  of  ance- 
any  other  planet  except  Venus  ;  at  such  a  time  he  casts 

253 


254 


A  Study  of  the  Sky. 


perceptible  shadows  of  terrestrial  objects.  Many  spots 
can  be  seen  on  his  surface,  even  with  a  telescope  of 
moderate  power  ;  by  watching  their  motion  the  time  of 
rotation  has  been  determined  ;  it  is  about  9hrs-  55min> 


FIG.  119.— JUPITER. 

The  swiftness  of  rotation  makes  the  delineations  of  its 
surface  markings  difficult. 

In  a  small  telescope  dark  belts  parallel  to  the  planet's 
equator  are  plainly  contrasted  with  the  general  yellowish- 
white  background.  A  large  telescope  reveals  a  wealth 
of  detail  and  a  richness  of  coloring,  which  call  forth  the 
admiration  of  the  beholder.  The  principal  belts  near 
the  equator  have  a  reddish  cast  ;  the  hue  is  modified 


Jupiter,   Saturn,    Uranus,   and  Neptune.         255 


from  time  to  time,  being  sometimes  salmon-colored  and 
at  others  a  rich  rose  pink.  There  are  many  subsidiary 
stripes  of  smaller  size  and  less  pronounced  color. 

The  whitish  portions  of  the  planet's  disc  are  by  no  whiteclouds 
means  devoid  of  interest.  They  look  like  aggregations 
of  cumulus  clouds,  such  as  deck  the  summer  sky.  One 
who  looks  down  from  the  top  of  a  mountain  upon  a 
layer  of  clouds  below  may  see  the  general  aspect  of  the 
Jovian  clouds.  Small  white,  dark,  and  red  spots  are 
strewn  here  and  there  over  the  surface. 

In  1878  there  suddenly  appeared  a  pink  spot  of  un- 
precedented dimensions  ;  the  length  is  given  as  30,000  red  spot, 
miles,  the  breadth  as  7,000.  In  another  year  its  hue 
was  a  full  Indian  red.  So  completely  did  it  dwarf  all 
other  recorded  spots  that  it  was  henceforth  known  as 
the  "  great  red  spot."  It  faded  away,  and  was  almost 
invisible  in  1883  and  1884.  Since  then  it  has  had 
irregular  spells  of  brightening,  but  has  never  recov- 
ered its  pristine  beauty.  The  time  of  rotation  of  the 
red  spot  is  not  the  same  as  that  of  the  adjacent  cloud- 
forms.  In  1890  a  large  spot  was  moving  directly 
toward  the  red  spot  ;  but  it  was  diverted  from  its 
course,  and  passed  by  at  one  side  of  the  spot.  After  it 
passed  by  it  did  not  return  to  its  original  course,  but 
remained  at  the  higher  latitude  into  which  it  had  been 
shunted  ;  it  passed  the  red  spot  at  the  rate  of  twenty 
miles  an  hour.  Professor  Keeler*  has  likened  the 
great  red  spot  to  a  sand  bank  in  a  river,  past  which  the 
flecks  of  foam  go  scurrying. 

The  red  belts  are  thought  to  be  cloudless  regions  ;   The  red  belts 
the  sunlight  striking  against  the  whitish  cloud-masses  is 
reflected  back  in  large  measure  ;   but  that  which  falls 
upon  the  red  rifts  between  the  clouds  is  not  so  well  re- 

*  Prof.  James  E.  Keeler,  of  the  Allegheny  Observatory. 


256 


A  Study  of  the  Sky. 


A  red  atmos- 
phere. 


Variable 
rotation. 


fleeted.  If  Jupiter's  atmosphere  is  red  and  the  white 
masses  are  clouds  floating  in  it  at  various  heights,  the 
general  appearances  are  explained.  What  we  have  called 
the  atmosphere  may  be  a  liquid  having  a  reddish  color. 
Not  only  do  the  different  parts  of  Jupiter's  cloud 
mantle  rotate  with  different  velocities,  but  even  the 


FIG.  120.— THK  GREAT  RED  SPOT. 

great  red  spot  has  not  kept  a  constant  period  of  rota- 
tion. At  first  the  whirling  of  the  planet  on  its  axis 
brought  it  around  in  9hrs-  55min-  34sec-  In  seven  years 
the  period  had  lengthened  seven  seconds.  If  it  had 
kept  the  new  rate  and  Jupiter  itself  had  been  a  solid 
rotating  at  the  old  rate,  it  would  have  gone  clear  around 


Jupiter,   Saturn,    Uranus,   and  Neptune.         257 

the  planet  in  less  than  six  years.  If  Australia  were  cut 
loose  from  its  moorings  and  drifted  toward  Africa,  we 
should  have  a  parallel  to  the  drift  of  the  red  spot. 
During  the  past  ten  years  (1886-96)  the  spot  has  ap- 
parently been  at  anchor. 

Though  changes  on  Jupiter's  face  are  not  very  rapid,    NO  permanent 
no  feature  is  permanent  either  in  form  or  position.      It  is  forms- 
then  a  reasonable  hypothesis  that  Jupiter  has  no  solid 
crust.       To   this    conclusion  some    other    facts    point. 
Though  Jupiter  is  1,300  times  as  large  as  the  earth,  it  is 
only  316  times  as  heavy  ;  it  is  therefore  only  one  fourth 
as  dense  and  may  plausibly  be  regarded  as  a  fluid  mass 
enveloped  in  a  deep  shell  of  cloud-laden  vapor. 

But   what  is  the  cause  of   the   abundant   supply   of 

1        i    ->      -ITTI       '•  T       •       i  1          1-1        i          Internal  heat. 

clouds  r  Why  is  not  Jupiter  s  atmosphere  clear  like  that 
of  Mars?  Clouds  cannot  be  formed  unless  there  is 
heat  to  produce  the  vapors  to  which  they  owe  their 
origin.  As  the  sunlight  is  only  one  twenty-seventh  as  in- 
tense as  ours,  the  necessary  heat  can  hardly  come  from 
that  source,  and  we  are  forced  to  conclude  that  Jupiter 
is  itself  a  warm  body.  This  conclusion  is  directly  in  line 
with  the  nebular  theory,  according  to  which  all  the 
planets  were  once  heated  bodies.  Jupiter,  being  much 
larger  than  the  other  planets,  would  cool  off  more  slowly 
and  require  a  longer  time  to  solidify.  But  if  Jupiter  be 
a  hot  body,  why  does  it  not  shine  with  some  such  vivid- 
ness as  a  fixed  star  manifests?  A  body  may  be  hot 
without  being  luminous  ;  a  kettle  of  boiling  water  would 
hardly  fill  the  office  of  a  student  lamp.  Jupiter  may  well 
be  regarded  as  a  semi-sun.  Its  interior  may  be  a  pasty  Asemisun 
mass  of  sufficient  consistency  to  give  considerable  per- 
manence of  location  to  such  an  object  as  the  great  red 
spot,  which  probably  owes  its  origin  to  a  disturbance  in 
the  depths  of  the  planet. 


258 


A  Study  of  the  Sky. 


The  moons. 


Discovery  of 
the  velocity 
of  light. 


Rotation  of 
the  satellites. 


Jupiter  is  accompanied  by  a  goodly  retinue  of  attend- 
ants, five  in  number.  Galileo  discovered  four  of  them, 
the  smallest  being  of  the  size  of  our  moon,  while  the 
largest  is  comparable  with  Mars.  They  are  designated 
by  Roman  numerals,  I  being  nearest  to  its  primary  and 
IV  farthest  away.  As  they  circle  round  the  planet,  they 
are  in  occultation  when  hiding  behind  him,  in  eclipse 
when  immersed  in  his  shadow,  and  in  transit  when 
crossing  his  disc.  The  times  of  all  these  phenomena 
are  given  in  the  '  *  Nautical  Almanac. ' ' 

Observations  of  them  in  the  seventeenth  century  led 
to  the  discovery  that  light  takes  an  appreciable  time  to 
fly  from  one  world  to  another.  How  this  came  to  pass 
is  not  difficult  to  understand.  Let  an  astronomer  observe 
the  times  of  a  number  of  eclipses  of  satellite  I  when 
Jupiter  is  in  opposition,  the  earth  at  that  time  being  at 
nearly  the  same  distance  from  him  for  several  weeks. 
Since  eclipses  occur  at  pretty  regular  intervals  it  will  not 
be  difficult  for  him  to  predict  from  his  observations  the 
times  at  which  fresh  eclipses  will  occur  several  weeks 
afterward.  Meanwhile  the  earth  and  Jupiter  are  getting 
farther  apart  and  the  predicted  eclipses  come  later  than 
expected.  The  reason  is  that  the  light  which  brings 
from  Jupiter  the  message  that  the  eclipse  has  begun  now 
takes  longer  to  perform  its  journey  than  it  did  when  the 
earth  and  Jupiter  were  nearer  together. 

Spots  have  been  seen  on  Jupiter's  satellites  at  times  ; 
attempts  have  been  made  to  find  their  times  of  rotation 
by  observing  these.  The  moons  have  also  appeared 
elongated.  If  one  looks  at  an  egg  one  hundred  feet 
away,  while  it  is  held  with  its  end  toward  him  the  egg 
appears  round  ;  when  it  is  held  sidewise  it  looks  oval. 
So  the  satellites,  if  really  oval,  will  appear  to.  be  out  of 
round  at  times.  The  high  tides  raised  upon  them  by 


Jupiter,   Saturn,    Uranus,  and  Neptune.         259 

Jupiter  may  have  elongated  them.  There  is  evidence 
that  some  of  them,  at  least,  keep  the  same  face  toward 
the  planet. 

The  fifth  satellite,  which  was  discovered  by  Barnard  The  fifth 
with  the  Lick  telescope  on  September  9,  1892,  is  much  satellite, 
smaller  than  the  others,  its  diameter  being  estimated  at 
one  hundred  miles.  It  is  less  than  70,000  miles  from 
Jupiter's  surface  and  occupies  nearly  twelve  hours  in 
making  one  revolution.  Only  the  largest  telescopes  can 
deal  successfully  with  it ;  the  other  moons  can  be  seen 
with  a  good  opera-glass.  People  of  extremely  acute 
vision  can  see  with  the  naked  eye  satellite  III,  which  is 
660,000  miles  from  Jupiter's  center,  or  IV,  which  is 
1,160,000  miles  away,  under  favorable  conditions. 

SATURN. 

The  ancients  regarded  Saturn  as  the  most  distant  of 
the  planets  because  of  his  dimness  and  the  slowness  of 
his  motion.  Little  did  they  imagine  that  this  dull-look- 
ing object  would  one  day  be  transformed  into  a  marvel 
which  would  ever  after  challenge  the  admiration  and 
awaken  the  enthusiasm  of  mankind.  Galileo  was  the 
first  to  perceive  that  it  was  no  ordinary  planet.  So  many 
imitators  had  followed  in  his  footsteps,  laying  claim  to 
greater  discoveries  than  he  had  made,  that  he  had  grown 
wary.  These  men  had  seen  twice  as  many  moons 
circling  around  Jupiter  as  Galileo  had  announced.  To 
baffle  them  he  set  forth  his  discovery  about  Saturn  in 
the  form  of  an  anagram.  This  procedure  had  the  de- 
sired effect,  and  the  pseudo-scientists  were  put  to  flight 
by  its  uncanny  array  of  disjointed  Latin.  The  emperor 
Rudolph  finally  prevailed  upon  Galileo  to  arrange  the 
letters  of  the  anagram  in  their  proper  order  ;  it  then 
became:  "Altissimum  planetam  tergeminum  obser- 


260 


A  Study  of  the  Sky. 


The  triple 
planet. 


The  mockery. 


Galileo's 
affliction. 


Huyghem 


The  ball 
and  ring. 


vavi "  (The  most  distant  planet  three-fold  I  have  ob- 
served). 

Galileo's  imperfect  telescope  had  shown  Saturn  as  a 
large  ball,  flanked  by  two  smaller  ones.  But  in  less 
than  two  years  a  change  took  place  which  was  a  sore 
trial  to  him.  He  says  : 

Looking  at  Saturn  within  a  few  days  I  found  it  solitary, 
without  the  aid  of  its  customary  stars,  and,  in  short,  exactly 
round  and  well  denned  like  Jupiter,  and  thus  it  still  remains. 
Now  what  can  be  said  of  so  strange  a  change  ?  Have  the  two 
lesser  stars  been  consumed  like  spots  on  the  sun  ?  Have  they 
suddenly  vanished  and  fled  away  ?  Or  has  Saturn  eaten  up  his 
children  ?  Or  was  the  appearance  a  delusion  and  a  snare,  with 
which  the  glass  has  deceived  me  and  many  others  who  have 
often  observed  with  me  ? 

He  never  divined  the  cause  of  their  disappearance. 
In  his  old  age  a  veil  was  drawn  over  his  eyes,  which  had 
done  so  much  in  unveiling  the  mysteries  of  the  skies, 
and  he  wrote  pathetically  : 

Alas  !  your  dear  friend  and  servant  is  entirely  blind.  Hence- 
forth this  universe,  which  I  have  enlarged  a  thousand  times  be- 
yond the  ideas  of  former  ages,  has  shrunken  for  me  into  the 
narrow  space  which  I  myself  fill  in  it.  So  it  pleases  God  ; 
it  shall  therefore  please  me  also. 

In  less  than  fifty  years  after  Galileo's  anagram  was 
given  to  the  world,  a  Dutch  astronomer,  Huyghens  by 
name,  set  another  one  afloat  in  the  sea  of  scientific 
thought.  His  alphabetical  agglomeration,  when  mar- 
shalled in  correct  array,  took  the  following  form  : 
' '  Annulo  cingitur,  tenui,  piano,  nusquam  cohaerente, 
ad  eclipticam  inclinato  "  (It  is  girdled  by  a  thin,  flat 
ring,  nowhere  touching,  inclined  to  the  ecliptic). 

This  admirably  correct  statement  renders  possible  an 
explanation  of  the  change  which  perplexed  Galileo. 
To  build  up  a  mental  picture  of  Saturn  we  must  imagine 


262 


A  Study  of  the  Sky. 


Phases  of 
the  rings. 


Divisions  of 
the  ring. 


a  rotating  ball  the  polar  axis  of  which  is  70,000  miles 
long,  while  its  equatorial  diameter  is  76,000  miles. 
Encircling  this  ball  and  lying  in  the  plane  of  its  equator 
is  a  thin  flat  ring,  the  outer  diameter  of  which  is 
173,000  miles,  the  inner  diameter  being  110,000  miles  ; 
its  thickness  probably  does  not  exceed  100  miles. 

As  Saturn  wheels  about  the  sun  in  his  appointed  path 
we  see  the  ring  in  different  positions.  Now  it  is  turned 
edgewise  to  us,  and  is  invisible  because  of  its  thinness. 
Again  it  is  turned  at  such  an  angle  that  an  imperfect 
telescope  shows  it  as  two  projections,  one  on  each  side 
of  the  central  ball.  The  greatest  angle  at  which  it  is  in- 
clined to  our  line  of  vision  is  28°.  Saturn  takes  twenty- 
nine  and  one  half  years  to  perform  one  revolution  about 
the  sun,  and  the  rings  are  edgewise  to  the  sun  twice 
during  a  revolution.  Midway  between  these  two  times 
they  are  in  the  best  position  for  observation.  Two 
favorable  years  are  1899  and  1914.  The  best  views  of 
Saturn  in  any  particular  year  are  obtainable  when  it  is 
at  opposition.  Its  mean  distance  from  the  sun  being 
886,000,000  miles,  it  is  then  about  800,000,000  miles 
from  us. 

Hitherto  we  have  spoken  of  "  the  ring."  It  is  really 
composed  of  three  concentric  rings  lying  in  the  same 
plane.  The  outermost  ring  is  10,000  miles  in  width, 
and  is  separated  from  the  middle  ring  by  a  space 
2,200  miles  wide,  which  is  called  "Cassini's  division." 
Other  fainter  divisions  have  been  glimpsed.  The  middle 
ring  is  17,500  miles  wide.  These  two  rings  are  of  the 
same  yellow  hue  as  the  ball  ;  the  innermost  ring  is  very 
dark,  and  is  known  as  the  cr£pe  ring,  or  gauze  ring.  It 
is  9,500  miles  wide  and  there  is  no  division  between  it 
and  the  ring  outside  of  it ;  between  its  inner  edge  and 
the  ball  is  a  space  of  7,000  miles. 


Jupiter,   Saturn,    Uranus,   and  Neptune.         263 

As  to  the  structure  of  the  rings  there  has  been  much 
discussion  ;  they  look  solid,  but  mathematicians  are  not  faring?  °f 
satisfied  with  appearances.  The  hypotheses  of  solidity 
and  fluidity  have  both  been  rejected,  because  the  rings 
would  not  be  stable,  but  would  be  destroyed  by  precipi- 
tation upon  the  ball.  Clerk  Maxwell,  the  famous  Eng- 
lish man  of  science,  has  shown  that  if  the  rings  are 
composed  of  myriads  of  little  bodies  too  small  to  be 
separately  visible  to  us,  the  system  is  stable.  So  ele- 
gant and  complete  were  Maxwell's  researches,  and  so 
cogent  was  his  train  of  reasoning,  that  the  Cambridge 
students  averred  that  he  paid  a  visit  to  Saturn  one 
evening,  and  cleared  up  the  mystery  with  his  own  eyes. 

The  largest  telescopes  have  given  no  ocular  proof  of 
the  correctness  of   Maxwell's   theory  ;  that  honor  has   Keeier's 

J  spectroscopic 

been  reserved  for  the  spectroscope,  which,  in  the  hands  observations, 
of  Keeler,  first  gave  a  satisfactory  demonstration.  The 
work  has  since  been  confirmed  by  others.  One  of  the 
offices  of  the  spectroscope  is  to  determine  whether  a 
body  is  approaching  us  or  receding  ;  it  is  now  possible 
to  measure  with  a  reasonable  degree  of  accuracy  the 
velocity  of  approach  or  recession.  If  Saturn's  ring- 
system  rotated  as  a  solid  mass  the  outer  edge  would 
move  more  swiftly  than  the  inner  one.  If,  on  the  other 
hand,  the  rings  are  composed  of  separate  small  bodies, 
those  bodies  which  are  near  the  inner  edge  must  travel 
more  rapidly  than  those  near  the  outer  edge,  because 
they  are  more  strongly  attracted  by  the  ball.  Dr. 
Keeier's  beautiful  photographs  of  the  spectrum  of  the 
ring-system  show  not  only  that  the  outer  edge  moves 
more  slowly  than  the  inner  one,  but  that  the  inter- 
mediate portions  move  with  intermediate  velocities  ; 
these  velocities  agree  with  what  would  be  expected  of 
bodies  moving  in  conformity  with  Kepler's  laws. 


264 


A  Study  of  the  Sky. 


Are  the  rings 
stable? 


The  gauze  ring. 


Thus  another  instance  is  added  to  the  list  of  cases 
where  mathematicians,  emboldened  by  confidence  in 
the  unerring  symbols  and  apparently  immutable  laws 
with  which  they  deal,  have  described  processes  going  on 
in  distant  worlds,  which  observers  have  afterward  veri- 
fied. 

Is  the  system  of  rings  really  stable  ?  What  must  be 
continually  happening  in  a  dense  swarm  of  bodies  mov- 
ing with  various  velocities  ?  Are  not  collisions  frequent  ? 
When  two  of  them  collide,  the  swifter  is  checked,  and 
the  slower  accelerated.  If  the  earth's  motion  about  the 
sun  were  suddenly  checked,  it  would  seek  a  new  path  of 
smaller  diameter.  If  its  velocity  were  increased  by  a 
blow  from  some  body  which  was  chasing  it,  the  earth 
would  swing  out  into  a  larger  orbit.  Collisions  in 
Saturn's  ring  must  therefore  cause  a  broadening  of  the 
ring,  since  some  of  the  bodies  are  getting  larger  veloci- 
ties and  others  smaller  ones. 

The  earliest  drawings  show  a  much  wider  space  be- 
tween the  ball  and  the  ring  than  now  exists,  and  thus 
bolster  up  the  theory,  but,  on  the  other  hand,  careful 
measures  of  the  dimensions  of  the  ring  system,  made 
during  the  past  fifty  years,  afford  no  evidence  of  enlarge- 
ment. 

The  dark  inner  ring  is  called  the  gauze  ring,  because 
it  is  not  opaque  ;  through  its  edge  one  can  sometimes 
see  the  ball.  Professor  Barnard  has  made  an  interesting 
observation  with  reference  to  its  transparency.  One  of 
Saturn's  moons,  which  had  been  eclipsed  in  the  shadow 
of  the  ball,  emerged  into  the  sunlight  for  a  while,  and 
then  plunged  into  the  shadow  of  the  dark  ring.  It  did 
not  disappear  at  once,  but  grew  fainter  till  it  en- 
countered the  shadow  of  the  inner  bright  ring,  then  it 
vanished.  The  gradual  diminution  of  its  brightness 


Jupiter,   Saturn,    Uranus,  and  Neptune.         26*5 


indicates  that  the  dark  ring  is  denser  on  its  outer  edge 
than  on  its  inner.  It  is  likely  that  the  small  bodies  are 
more  closely  crowded  together  near  one  edge  than  at 
the  other. 

The   ball,    though    large,    is    not  heavy  ;  its  average 

.         '  11-  The  ball. 

density  is  only  one  eighth  that  of  the  earth,  being  con- 
siderably less  than  that  of  water.  The  equator  is  brighter 
than  the  regions  on  each  side,  and  faint  belts  are  some- 
times seen  well  up  toward  the  poles.  There  is  but  little 
change  in  appearance  from  year  to  year.  In  December, 
1876,  a  small  white  spot  suddenly  burst  forth  near  the 
equator,  and  was  visible  for  a  month  ;  the  planet's  rota- 
tion carried  the  spot  around  in  10  hrs-  i4min-  The  placid 
cloud-mantle  in  which  the  ball  is  enveloped  hides  most 
of  the  commotion  within  ;  the  interior  does  not  seem  to 
be  in  such  a  state  of  activity  as  Jupiter  manifests. 

Eight  satellites  accompany  Saturn.  Their  names, 
from  the  outermost  inward,  are  :  lapetus,  Hyperion, 
Titan,  Rhea,  Dione,  Tethys,  Enceladus,  and  Mimas. 
Titan,  the  largest,  is  four  times  as  big  as  our  moon,  and 
occupies  nearly  sixteen  days  in  a  revolution.  The  exist- 
ence of  Cassini's  division  in  the  rings  has  been  attrib- 
uted to  Titan's  pull,  which  so  disturbed  the  moonlets 
which  once  were  there  that  they  forsook  their  paths, 
lapetus  is  2,225,000  miles  from  the  planet's  center,  and 
looks  twice  as  bright  when  it  is  on  one  side  of  it  as  when 
on  the  other  side.  This  is  explained  by  the  hypothesis 
that  a  large  part  of  the  surface  is  much  darker  than  the 
rest,  and  that,  like  our  moon,  it  keeps  the  same  face  to- 
ward its  primary. 

URANUS. 

Uranus  was  discovered  by  Sir  William  Herschel.  This  sir  william 
remarkable  man,   to  whom   astronomy  owes  so  much,    Herschel- 
was  a  native  of  Hanover.     His  father  was  a  musician, 


266 


A  Study  of  the  Sky. 


A  musician. 


He  grinds 
mirrors. 


and  the  son  was  diligently  instructed  in  that  art.  At  the 
age  of  seventeen  he  was  oboist  in  a  regiment  of  Hano- 
verian guards  ;  but  two  years  afterward  he  deserted,  and 
employed  his  musical  talents  in  other  directions.  He 
speedily  rose  to  prominence,  and  in  a  few  years  became 
organist  of  the  Octagon  Chapel  at  Bath.  The  society  to 
which  he  was  thus  introduced  was  brilliant  and  fashion- 
able, and  his  talents  brought  him  prominence  and  pros- 
perity. But  despite  manifold  professional  engagements, 
which  would  have  entirely  absorbed  the  energies  of  an 

ordi  nary  m  an, 
his  restless  mind 
reached  out  into 
other  fields.  Studies 
in  Italian,  Greek, 
pure  mathematics, 
optics,  and  astron- 
omy failed  to  satiate 
his  thirst  for  knowl- 
edge. 

When  thirty-five 
years  of  age  he  ob- 
tained the  use  of  a 
small  telescope.  Its 
revelations  fired  him 
with  a  purpose  to 
obtain  a  knowledge 
of  the  construction  of  the  heavens.  He  set  himself  reso- 
lutely at  the  task  of  making  a  larger  telescope.  His 
pertinacity  knew  no  limit.  Mirror  after  mirror  was 
ground  and  polished.  His  sister  Caroline,  who  was  his 
constant  attendant,  writes  :  ' '  My  time  was  taken  up 
with  copying  music  and  practicing,  besides  attendance 
upon  my  brother  when  polishing,  since  by  way  of  keep- 


FIG.  122.— SIR  WILLIAM  HERSCHEL. 


Jupiter,   Saturn,    Uranus,  and  Neptune.         267 

ing  him  alive  I  was  constantly  obliged  to  feed  him  by 
putting  the  victuals  by  bits  into  his  mouth."  By  day 
he  ground  mirrors  and  gave  music  lessons  ;  in  the  even- 
ings he  conducted  concerts  and  oratorios,  running  out 
at  intervals  to  look  through  a  telescope  ;  at  night  he 
scanned  the  sky. 

After  seven  years  spent  in  this  way  Uranus  swam  into  Uranus  swims 
his  ken  on  March  13,  1781.  He  tells  of  the  discovery  into  his  ken. 
thus  :  ' '  On  this  night,  in  examining  the  small  stars 
near  Eta  Geminorum  I  perceived  one  visibly  larger 
than  the  rest.  Struck  with  its  uncommon  appearance 
I  compared  it  with  Eta  Geminorum  and  another  star, 
and  finding  it  so  much  larger  than  either,  I  suspected  it 
to  be  a  comet."  Professional  astronomers  began  to 
observe  the  new  body,  and  later  computations  showed 
that  its  orbit  was  nearly  a  circle  ;  it  was  therefore  no 
comet,  but  a  new  planet. 

The  discovery  aroused  great  enthusiasm,  since  all  the 

,  c  *•  HerschePs 

other  planets  had  been  known  trom  the  earliest  an-  prosperity, 
tiquity.  Herschel  was  at  once  brought  into  royal  favor, 
received  a  pension,  and  was  given  all  needed  funds  for 
constructing  a  twenty-foot  reflecting  telescope,  which 
was  much  larger  than  any  hitherto  made.  With  this 
instrument  and  a  forty-foot,  built  afterward,  Herschel 
carried  forward  the  wonderful  series  of  observations 
which  made  him  supreme  among  astronomical  observers 
of  all  ages.  His  faithful  sister  Caroline  was  his  indefati- 
gable assistant,  recording  his  observations  at  night,  as 
he  dictated  them  to  her,  and  making  tedious  calculations 
by  day.  Herschel  and  Uranus  were  discovered  sim- 
ultaneously ;  the  importance  of  the  discovery  of  the 
man  is  a  sufficient  excuse  for  devoting  so  much  atten- 
tion to  him. 

Of  Uranus  little  is  known  which  cannot  be  expressed 


268 


A  Study  of  the  Sky. 


Details  about 
Uranus. 


Short  and 
simple  annals. 


Its  discovery. 


in  cold  figures.  Its  distance  from  the  sun  is  1,780,000,- 
ooo  miles,  and  its  diameter  is  32,000  miles.  Its  time  of 
revolution  is  eighty-four  years.  It  is  visible  to  the 
naked  eye,  and  even  the  most  powerful  telescopes  show 
simply  a  greenish  disc  on  which  there  are  faint  belts.  A 
dense  atmosphere  produces  marked  absorption  bands  in 
its  spectrum.  What  is  beneath  the  atmosphere  no  one 
can  tell.  Four  satellites  attend  it ;  strange  to  say,  the 
plane  in  which  their  orbits  lie  is  so  tipped  up  as  to  be 
nearly  perpendicular  to  the  plane  of  the  planet's  orbit. 
The  moons  also  revolve  from  east  to  west,  while  all 
other  satellites  heretofore  considered  go  from  west  to 
east. 

NEPTUNE. 

More  than  1,000,000,000  miles  beyond  Uranus  plods 
slow-footed  Neptune,  the  outpost  of  the  solar  system. 
Its  mean  distance  from  the  sun  is  2,792,000,000  miles, 
and  its  diameter  is  35,000  miles.  An  opera-glass  will 
render  it  visible  ;  it  exhibits  in  a  large  instrument  a 
small  greenish  disc  on  which  no  details  can  be  seen. 
Like  Uranus  it  is.  enveloped  in  a  dense  atmosphere, 
through  which  struggles  sunlight  only  -^  as  intense  as 
ours.  Its  one  moon  is  a  tiny  speck  of  light,  and  is 
supposed  to  be  about  as  big  as  ours.  Like  the  moons 
of  Uranus  it  revolves  backward  in  its  orbit.  Neptune 
requires  165  years  to  complete  a  journey  around  the 
sun. 

The  circumstances  of  its  discovery  are  of  high  interest 
and  involve  one  of  the  greatest  triumphs  of  mathemati- 
cians. The  discovery  arose  from  the  strange  behavior 
of  Uranus,  which  refused  to  follow  the  path  which  had 
been  laid  down  for  it  by  the  mathematicians.  After  they 
had  thought  that  it  was  securely  ensnared  it  persisted  in 
breaking  the  chains  of  their  analysis,  wandering  into 


Jupiter,   Saturn,    Uranus,   and  Neptune.         269 

by  and  forbidden  paths.  Sixty  years  after  its  discovery 
it  had  gone  so  far  astray  that  no  one  could  doubt  that 
something1  was  wrong  ;  to  be  sure,  the  theoretical  and 
the  actual  planet  were  so  close  together  that  the  unaided 
eye  would  see  them  as  one  body,  but  the  discrepancy  An  intolerable 

.  .  discrepancy. 

was  intolerable  to  a  mathematical  mind. 

So  firmly  convinced  were  astronomers  of  the  accuracy 
and  universality  of  Newton's  law  of  gravitation  that 
they  became  convinced  that  the  observed  irregularities 
must  be  due  to  the  attraction  of  some  other  body,  which 
pulled  Uranus  away  from  its  proper  path.  It  is  a  prob- 
lem of  no  mean  difficulty  to  compute  the  effect  of  one 
planet's  pull  on  another,  when  the  masses  and  relative 
positions  of  the  bodies  are  known.  How  much  A  difficult 

1         frr       1  r    i-  •          1  1  problem. 

greater  the  difficulty  of  discovering  the  mass  and  success- 
ive positions  during  a  series  of  years  of  an  unknown 
body,  which,  as  the  upshot  showed,  was  more  than 
1,000,000,000  miles  away  from  Uranus.  Several  eager 
minds  attacked  the  problem,  but  found  it  too  difficult 
for  their  powers. 

Mr.  J.  C.  Adams,  a  student  of  the  University  of  Cam-  Adams 
bridge,  resolved  to  look  into  the  matter  as  soon  as  his 
final  examinations  were  over.  In  January,  1843,  having 
graduated  as  senior  wrangler,  he  set  to  work.  In  Octo- 
ber, 1845,  he  communicated  his  results  to  the  astrono- 
mer royal,  who  naturally  thought  it  very  improbable  that 
a  young  and  unknown  student  should  have  solved  so 
profound  a  problem.  He  looked  over  the  papers,  and 
seeing  that  they  gave  evidence  of  careful  research, 
wrote  to  their  author  concerning  an  obscure  point  in  the 
investigation.  Unfortunately  Mr.  Adams  did  not  reply 
at  once,  and  his  communication  was  pigeon-holed. 

Meanwhile  a  young  Frenchman,  Leverrier,  had  con-   Leverrier 
centrated  his  marvelous  powers  upon  the  problem.      In 


270 


A  Study  of  the  Sky. 


Challis  hunts. 


Galle  finds  it. 


November,  1845,  he  sent  a  paper  to  the  French  Acad- 
emy, in  which  he  showed  that  no  known  causes  of  error 
would  account  for  the  wanderings  of  Uranus.  A  second 
paper  in  June  of  the  next  year  assigned  to  the  disturbing 
body  a  definite  place  in  the  zodiac.  When  this  news 
reached  England  the  astronomer  royal  was  astonished  to 
find  that  Adams  and  Leverrier  were  in  substantial 
agreement. 

He  at  once  wrote  to  Professor  Challis  of  Cambridge, 
asking  him  to  search  for  the  suspected  planet.  Professor 
Challis  was  not  very  enthusiastic,  but  set  about  the  work 
with  due  regard  to  thoroughness  and  to  leisurely  dignity. 
He  began  to  take  the  positions  of  all  visible  stars  in  the 
suspected  region,  going  over  the  same  locality  three 
times.  It  was  his  intention  at  some  convenient  season 
to  prepare  a  map  from  each  night's  work,  and  by  com- 
paring them  to  find  out  if  any  one  of  the  objects  noted 
had  moved. 

While  he  was  engaged  in  manipulating  his  astronomi- 
cal drag-net,  Leverrier,  who  knew  nothing  of  the  work 
of  the  Englishmen,  completed  his  investigations  and  re- 
quested Galle,  director  of  the  observatory  at  Berlin,  who 
was  already  in  possesssion  of  an  excellent  star  chart,  to 
look  in  a  certain  place  ;  there  he  would  find  the  planet. 
The  letter  was  received  on  September  23,  and  on  the 
same  night  Galle  came  upon  the  planet  within  a  degree 
of  the  predicted  place.  When  the  news  reached  Eng- 
land Professor  Challis  bestirred  himself,  looked  over  his 
note-books,  and  found  that  he  had  observed  the  planet 
on  August  4  and  August  1 2.  Had  he  been  prompt  in 
comparing  his  results,  he  would  have  detected  the  new 
body  before  Galle  looked  for  it  ;  but  his  burst  of  speed 
came  after  the  race  was  over.  Thus  did  confidence  and 
energy  win  the  victory  over  doubt  and  delay. 


CHAPTER  XVI. 

COMETS  AND  METEORS. 

"  Stranger  of  Heaven,  I  bid  thee  hail ! 
Shred  from  the  pall  of  glory  riven, 
That  flashest  in  celestial  gale — 

Broad  pennon  of  the  King  of  Heaven." 

—Hogg. 

"And  certain  stars  shot  madly  from  their  spheres, 
To  hear  the  sea-maid's  music." 

— Shakespeare. 

FEW  astronomers  devote  themselves  to  searching  for 
comets  ;  such  work  requires  extreme  patience,  involves  Comet  huntl"g- 
irregular  hours  of  work,  requires  very  little  mathemati- 
cal training,  and  is  quite  monotonous  except  at  the  su- 
preme moment  of  discovery.  If  the  moon  is  bright  in 
the  early  evening  the  comet  hunter  waits  till  it  has  set. 
Night  after  night  he  shifts  the  pointer  on  his  alarm  clock 
and  alters  his  hours  for  sleep.  When  once  at  his  tele- 
scope he  sweeps  over  a  certain  part  of  the  sky,  keeping 
his  eye  closely  confined  at  the  eyepiece,  that  nothing 
may  escape.  If  a  faint  wisp  of  nebulous  light  comes 
into  view  he  inspects  it  with  care  ;  if  he  does  not  recog- 
nize it  he  looks  in  his  catalogue  of  nebulae  to  see  if  it  is 
described  there.  If  not,  he  concludes  that  it T  .iew,  and 
watches  it  for  an  hour  or  so  to  see  whether  it  appears  to 
move  among  the  surrounding  stars.  Any  motion  be- 
trays its  cometary  nature  ;  if  it  remains  at  rest  it  is  a 
nebula.  A  comet  may  also  be  discovered  by  an  astro- 
nomical photographer,  who  finds  its  image  impressed 
upon  one  of  his  plates. 


272 


A  Stiidy  of  the  Sky. 


The  comet 
ensnared. 


Three  obser- 
vations. 


The  new  comet  is  promptly  announced,  so  that  obser- 
vations of  it  may  begin  at  once.  Its  right  ascension  and 
declination  are  measured  by  comparing  it  with  known 
stars  which  lie  along  its  path.  The  star  catalogues  con- 
tain the  places  of  several  hundred  thousand  stars,  so 
that  a  known  one  can  always  be  found  in  the  vicinity  of 

the  comet.  With 
his  micrometer, 
which  has  been 
previously  de- 
scribed, the  as- 
tronomer meas- 
ures the  position 
of  the  comet  with 
reference  to  the 
star.  He  may 
find,  for  instance, 
that  the  comet's 
right  ascension  is 
29.42sec-  greater 
than  that  of  the 
star,  and  the  dec- 
1  i n  a t  i  o  n  is  4' 
1 3".  2  less.  Ap- 
plying these 

FIG.  123.— DISCOVERY  OF  A  COMET  BY  PHOTOGRAPHY,  quantities   to    the 

known  right  ascension  and  declination  of  the  star  he  ob- 
tains the  comet's  place.  After  a  comet's  place  has  been 
measured  three  times,  a  preliminary  orbit  of  it  is  com- 
puted and  its  location  is  predicted  for  a  month  or  so  in 
advance,  so  that  observers  may  more  readily  keep  on 
its  track.  When  a  large  number  of  observations  have 
been  made,  a  more  accurate  computation  of  its  path  is 
executed. 


Comets  and  Meteors. 


273 


Its  orbit  must  be  a  parabola,  or  an  ellipse,  or  an  hy- 
perbola ;  so  Newton's  law  demands.  Most  comets  move 
in  orbits  so  nearly  parabolic  that  it  is  customary  to  com- 
pute the  first  orbit  on  the  assumption  that  it  is  a  parab- 
ola. If  the  comet  refuses  to  follow  this  curve,  it  is 
generally  found  to  move  in  an  ellipse.  Hyperbolic  paths 
are  rare.  While  an  ellipse  is  a  closed  curve,  a  parabola 
or  an  hyperbola  is  not. 

Some  elementary  notions 
about  celestial  mechanics  as- 
sist one  in  understanding  the 
history  of  these  wanderers, 
prior  to  their  introduction  to 
us.  If  one  of  them  is  mov- 
ing slowly  along  in  space, 
millions  of  millions  of  miles 
from  the  sun,  the  attraction 
of  the  latter  compels  it  to  fall 
toward  him.  Were  the  sun 
and  comet  originally  at  rest, 
the  comet  would  make 
straight  for  the  sun  ;  but  as 
both  are  moving,  the  comet  FlG-  '^.-PATHS  OF  COMETS. 
comes  down  in  a  parabolic  curve,  whisks  around  the 
sun,  and  is  of!  again,  never  to  return. 

If  the  comet,  while  passing  through  the  solar  system, 
happens  to  come  near  one  of  the  larger  planets,  its  path 
may  be  seriously  altered.  If  Jupiter,  for  example,  is  so 
situated  with  reference  to  the  comet  that  its  attraction  in- 
creases the  latter' s  velocity,  the  orbit  will  become  an 
hyperbola.  But  if  Jupiter  diminishes  the  stranger's  ve- 
locity, the  orbit  changes  to  an  ellipse,  and  the  comet  is 
compelled  to  become  an  attache  of  the  sun.  Jupiter's 
brigandage  has  led  to  the  capture  of  several  small  com- 


The  shape  of 
the  orbit. 


274 


A  Study  of  the  Sky. 


Groups  of 
comets. 


The  make-up 
of  a  comet. 


Light  and  airy 


ets,  which  are  denominated  his  family.  Saturn,  Uranus, 
and  Neptune  have  also  indulged,  to  a  lesser  extent,  in  this 
piratical  business. 

There  are  a  few  instances  of  groups  of  comets  which 
have  nearly  the  same  paths  during  their  visibility,  but 
revolve  in  different  times.  The  comets  of  1668,  1843, 
1880,  1882,  and  1887  form  such  a  group.  Each  of  them 
passes  close  to  the  sun's  surface,  and  is  therefore  ex- 
posed to  a  tremendous  heat,  and  also  subjected  to  a  power- 
ful tidal  strain.  A  modern  French  mathematician  has 
proved  that  if  a  comet  be  disrupted  in  this  manner,  its 
fragments  will  afterward  pursue  similar  paths. 

Comets  are  erratic,  not  only  in  their  motions,  but  also 
in  their  appearances  ;  they  are  continually  doing  some- 
thing outrt.  The  peculiarities  of  their  behavior  must 
be  attributed  largely  to  their  make-up.  They  are  not 
compact  masses  of  matter  like  the  earth  or  the  moon,  but 
rather  loose  aggregations  of  small  bodies,  which  fly 
along  together  like  so  many  grape-shot.  These  bodies 
must  sometimes  be  reduced  to  liquids,  when  exposed  to 
intense  solar  heat,  and  carry  with  them  a  certain  amount 
of  gaseous  matter.  Of  their  sizes  no  certain  estimate 
can  be  made,  but  they  probably  vary  from  the  merest 
particles,  like  grains  of  sand,  to  more  substantial  masses 
as  big  as  a  house,  or  even  larger.  The  connection  be- 
tween certain  comets  and  meteoric  swarms  renders  it 
almost  certain  that  comets  are  largely  bunches  of  small 
bodies. 

Large  as  comets  are,  they  are  comparatively  insignifi- 
cant in  mass  and  density.  As  they  dash  along  over  the 
face  of  the  sky  they  scarcely  obscure  even  the  faintest  of 
the  stars  which  lie  behind  them.  Though  their  texture 
is  so  diaphanous,  yet  the  gases  which  accompany  the 
more  solid  portions  are  sometimes  of  sufficient  refract- 


Comets  and  Meteors.  275 

ive  power  to  bend  by  a  minute  amount  the  rays  of  light 
coming  through  them  from  the  stars  beyond.  Were 
comets  as  dense  as  planets,  some  of  them  would  derange 
the  orbits  of  the  planets  seriously  by  their  attraction. 
It  has  been  estimated  that  100,000  of  the  largest  comets 
put  together  would  not  weigh  as  much  as  the  earth. 

Having  premised  these  facts   we  are  better  able  to   changesof 
understand  the  changes  which  take  place  in  a  comet's  appearance, 
appearance  as  it  approaches  the  sun  and  recedes  from 
him  again.      As  it  draws  near,  the  increasing  heat  and 
the  electrical  influences  wnich  the  sun  probably  exer- 
cises   cause    it    to    brighten.      The    densest   portion    of 
the  cometary  mass,  which  is  called  the  nucleus,  comes 
into  prominence  as  a  hazy  mass,    more    compact    and 
brilliant  than  the  surrounding  nebulosity. 

The  tail  forms  gradually,  and  prudently  keeps  on  the 
side  away  from  the  sun.  The  nucleus  seems  to  be  the 
seat  of  the  greatest  activity  ;  it  spurts  out  jets  toward 
the  sun,  or  throws  off  masses  of  vapor,  which  are  driven 
back  into  the  tail.  The  entire  body  of  the  comet  is 
affected  to  an  extent  which  would  be  impossible  were  it 
a  single  compact  mass.  After  the  comet  has  passed 
perihelion  the  disturbances  die  away ;  the  nucleus  grows 
fainter  and  more  sluggish  in  its  actions ;  the  tail  shortens 
up  and  disappears.  After  a  few  weeks  or  months  only 
a  pale  nebular  gleam  remains,  which  soon  vanishes. 
Such  is  a  crude  outline  of  the  general  behavior  of  a 
comet  of  moderate  size  and  average  friskiness. 

We  proceed  to  consider  various  details.  First  as  to 
the  jets  and  envelopes.  These  are  rarely  seen  in  faint  envelopes, 
comets,  but  are  conspicuous  in  bright  ones.  The  sun- 
ward side  of  the  nucleus  is  the  seat  of  forces  which 
project  bright  jets  ;  as  the  jets  rise  higher  and  higher 
they  spread  out  and  become  lost  in  the  general  nebu- 


276 


A  Study  of  the  Sky. 


Umbrella-like 
forms. 


The  tail. 


losity  of  the  comet's  head.  The  formation  of  envelopes 
is  a  less  violent  and  more  orderly  procedure.  These 
umbrella-shaped  forms  rise  toward  the  sun  one  after 
another  at  intervals  of  some  hours,  as  if  the  comet 
were  endeavoring  to  protect  itself  from  the  solar  radia- 
tion. As  they  ascend  they  expand  and  grow  fainter  till 
their  distinctive  appearance  is  lost,  like  that  of  the  jets. 
The  magnificent  trains  which  accompany  bright 


FIG.  125.— JETS  AND  ENVELOPES. 

comets  are  their  most  characteristic  features.  Often 
they  are  tens  or  even  hundreds  of  millions  of  miles 
in  length.  Occasionally  they  are  nearly  straight,  but 
usually  they  have  the  graceful  contour  of  the  plume  on 
a  knight's  crest.  The  material  projected  toward  the 
sun  by  the  jets  and  envelopes  encounters  a  resistance 
which  destroys  its  original  motion,  and  drives  it  back- 
ward past  the  nucleus  into  the  tail.  If  a  locomotive 
puffed  its  smoke  forward  instead  of  upward,  it  would  be 
swept  backward  in  much  the  same  fashion. 


Comets  and  Meteors.  277 

The  repellent  force,  which  triumphs  so  signally  over 
the  pull  of  the  sun  on  these  little  solid,  liquid,  and 
gaseous  emanations,  is  supposed  to  be  electrical.  In 
any  physical  •  laboratory  may  be  seen  pith-balls  and 
light  strips  of  paper,  which  are  lifted  by  electrical  forces 
in  opposition  to  the  force  of  gravity.  In  a  similar  way 
the  lightest  portions  of  a  comet  may  be  driven  off  by  an 
electrical  repulsion  originating  in  the  sun,  while  the 
heavier  portions  are  dominated  by  his  attraction. 

The  spectroscope  certifies  to  the  presence  of  a  few 
known  elements  in  comets.  The  predominant  gases  Different 

materials. 

seem  to  be  hydro-carbons,  which  are  compounds  of 
hydrogen  and  carbon.  Sodium  and  iron  have  been 
certainly  identified,  and  magnesium  and  calcium  are 
thought  to  be  present.  What  happens  to  these  differ- 
ent materials  as  they  are  being  driven  off  by  the 
electrical  repulsion  ?  Manifestly  the  lightest  elements 
attain  the  greatest  velocity ;  moderately  heavy  ones 
move  with  less  velocity,  and  the  heaviest  with  still  less. 
These  motions,  combined  with  the  orbital  motions  of 
comets,  cause  various  degrees  of  curvature  in  their  tails. 

There  are  three  special  types  of  tails.  Tails  of  the  first 
type  are  nearly  straight  and  point  almost  directly  away  Typesoftails- 
from  the  sun.  They  are  believed  to  be  composed  largely 
of  hydrogen.  The  majority  of  the  trains  belong  to  the 
second  type,  and  are  gracefully  curved  ;  here  the  repul- 
sive force  has  less  effect  than  before,  as  the  particles  on 
which  it  acts  are  heavier.  Tails  of  this  type  are  com- 
posed of  hydro-carbons.  The  third  type  of  tail  is  un- 
common ;  it,  too,  is  plume-like,  but  it  curves  very 
sharply  at  the  comet's  head,  and  trails  behind  the  nu- 
cleus as  the  latter  moves  swiftly  in  its  appointed  path. 
Iron  vapor  is  thought  to  be  present  in  such  tails. 

The  appearances  of  the  three  types  are  aptly  repre- 


278 


A  Study  of  the  Sky. 


The  smoke  of 
a  locomotive. 


Anomalous 
tails. 


sented  by  the  smoke  which  issues  from  a  freight  engine 
moving  in  a  quiet  atmosphere  at  a  moderate  speed.  If 
the  steam  pressure  is  very  high,  the  puffs  of  smoke  go 
nearly  straight  up  ;  if  the  pressure  is  only  moderate,  the 
stream  of  smoke  forms  a  curving  plume;  when  the 
steam  is  nearly  shut  off  the  smoke  trails  lazily  behind  the 
smoke-stack. 

Some  comets  exhibit  more  than  one  type  of  tail  ;  even 
so  strange  a  phenomenon  as  a  tail  pointing  directly  to- 
ward the  sun  has  been  observed.  Wonderful  changes 
have  been  noticed,  as  in  the  case  of  Swift's  bright  comet 
of  1892.  On  April  4  its  tail  was  straight  and  twenty 
degre£s  in  length,  but  consisted  of  two  distinct  branches 
lying  close  together.  On  the  next  night  a  third  tail  was 
seen  between  the  other  two  ;  each  of  the  three  appeared 
to  be  composed  of  several,  so  that  the  whole  looked  like 
a  fan  partially  opened.  Within  twenty-four  hours  more 
one  tail  vanished,  and  the  other  two  joined  their  bound- 
aries. One  of  these  then  grew  bright  at  the  expense  of 
the  other,  and  finally  split  up  into  half  a  dozen  branches. 
These  are  the  most  noteworthy  of  the  changes  which 
took  place  in  five  days. 

The  particles  which  are  driven  off  into  the  tails  are 

Fate  of  comets,    lost.     A  periodic  comet,  i.   <?. ,  one  which  moves  in  an 

ellipse  and  returns  at  stated  intervals,  loses  some  of  its 

substance   at   each    perihelion   passage,    and    must    be 

wasted  away  in  time. 

Comets  are  sometimes  accompanied  by  smaller  com- 
panions. In  1889  one  was  seen  which  had  no  less  than 
four  of  these  attendants  ;  two  of  them  were  very  faint, 
and  did  not  last  long  ;  for  a  while  the  other  two  were 
veritable  twins,  and  bore  a  striking  resemblance  to  the 
main  comet.  Like  foolish  children  they  cut  the  maternal 
apron  strings  and  began  to  move  away  ;  this  move  sealed 


Companions. 


280 


A  Study  of  the  Sky. 


Changes  of 
brightness. 


Superstitious 
terror. 


Collisions. 


the  fate  of  one  of  them,  which  soon  faded  into  invisibil- 
ity. The  other  made  a  brave  show  for  a  time,  but  came 
back  in  a  few  weeks  with  a  swelled  head  and  no  tail. 
The  moral  is  obvious. 

Though  the  brightness  of  a  comet  generally  changes 
with  considerable  regularity  as  its  distances  from  the  sun 
and  earth  vary,  there  are  often  anomalous  variations, 
which  are  best  explained  by  electrical  discharges  between 
the  small  masses  of  which  it  is  made  up.  The  existence 
of  such  discharges  is  not  merely  conjectured.  During 
the  past  few  years  spectroscopic  observations  of  comets 
have  gone  hand  in  hand  with  laboratory  experiments 
upoij  gases  confined  in  Geissler  tubes,  and  lit  up  by  elec- 
tric discharges.  A  mass  of  evidence  has  thus  been  ac- 
cumulated which  cannot  be  set  aside  ;  unfortunately  it 
is  too  technical  to  be  reproduced  here.*  Suffice  it  to  say 
that  the  coincidences  between  electrical  appearances  pro- 
duced in  the  laboratory  and  those  observed  in  the  spec- 
tra of  comets  are  very  complete. 

It  is  well  known  that  in  past  centuries  comets  were 
objects  of  superstitious  terror,  not  only  to  the  ignorant, 
but  even  to  the  higher  classes  of  society.     The  comet  of 
1528  is  thus  described  by  Ambrose  Pare  : 

This  comet  was  so  horrible,  so  frightful,  and  it  produced 
such  great  terror  in  the  vulgar  that  some  died  of  fear  and  others 
fell  sick.  It  appeared  to  be  of  excessive  length,  and  was  of  the 
color  of  blood.  At  the  summit  of  it  was  seen  the  figure  of  a 
bent  arm,  holding  in  its  hand  a  great  sword,  as  if  about  to 
strike.  At  the  end  of  the  point  there  were  three  stars.  On 
both  sides  of  the  rays  of  this  comet  were  seen  a  great  number 
of  axes,  knives,  blood-colored  swords,  among  which  were  a 
great  number  of  hideous  human  faces,  with  beards  and  brist- 
ling hair. 

Though  some  unaccountable  superstitions  still  survive 

*  See  Schemer's  "  Astronomical  Spectroscopy,"  pages  207-22. 


Comets  and  Meteors.  281 

among  fairly  educated  members  of  enlightened  com- 
munities, very  few  of  them  are  connected  with  com- 
ets. But  there  is  apprehension  in  many  quarters  con- 
cerning the  results  of  a  collision  between  a  comet  and 
the  earth.  The  fear  is  that  the  great  heat  generated  by 
the  impact  would  blast  the  earth' s  surface  as  effectually 
as  if  it  were  tossed  into  a  gigantic  furnace,  and  would 
dissolve  all  its  inhabitants  in  the  twinkling  of  an  eye.  It  No  reat 
appears  from  what  we  have  learned  of  the  constitution  of  danger, 
comets  that  nothing  of  the  sort  is  to  be  feared.  Astron- 
omers would  be  delighted  if  any  ordinary  comet  should 
run  into  the  earth,  for  there  would  be  a  shower  of  fall- 
ing stars  most  beautiful  to  behold.  A  very  large  cpmet 
might  make  more  trouble  ;  for  such  an  one  probably  con- 
tains a  good  supply  of  metallic  masses,  which  would  come 
through  the  air  without  being  consumed.  Fortunately 
they  would  not  be  close  together,  for  stars  have  been 
seen  shining  with  undiminished  splendor  through  the 
nuclei  of  large  comets  ;  a  city  as  large  as  Chicago  might 
catch  only  a  few  of  the  celestial  missiles.  Some  of  them 
might  be  as  large  as  houses  and  cause  decided  havoc 
where  they  struck.  The  celestial  spaces  are  so  vast  in 
comparison  with  the  bodies  which  traverse  them  that 
there  is  little  danger  to  be  apprehended  from  comets. 

In  November,  1892,  there  was  a  comet  scare,  caused  A  comet  scare, 
by  the  apprehension  that  Biela's  comet*  was  about  to 
dash  against  our  planet.     The  fright  inspired  in  certain 
localities  is  evidenced  by  the  following  press-dispatch 
from  Atlanta,  Georgia  : 

The  fear  which  took  possession  of  many  citizens  has  not  yet 
abated.  The  general  expectation  hereabouts  was  that  the 
comet  would  be  heard  from  on  Saturday  night.  As  one  result 
the  confessionals  of  the  two  Catholic  churches  were  crowded 

*  Holmes's  faint  comet  was  erroneously  thought  to  be  a  return  of  Biela's. 


282 


A  Study  of  the  Sky. 


yesterday  evening.     As  the  night  advanced  there  were  many 

who  insisted  that  they  could  detect  a  change  in  the  atmosphere. 

The  stifling  air    The  a*r>  tnev  sa^>  was  stifling.     It  was  wonderful  to  see  how 

many  persons  gath- 
ered from  different 
sections  of  the  city 
around  the  news- 
paper offices,  with 
substantially  the  same 
statement.  As  a 
consequence  many 
families  of  the  better 
class  kept  watch  all 
night,  in  order  that 
if  the  worst  came  they 
might  be  awake  to 
meet  it.  The  orgies 
around  the  colored 
churches  would  be 
laughable,  were  it  not 
for  the  seriousness 
with  which  the  wor- 
shipers take  the  mat- 
ter. To-night  (Sat- 
urday) they  are  all 
full,  and  sermons 
suited  to  the  terrible 
occasion  are  being  de- 
livered. 

So   great    is    the 
number  of  splendid 
comets  the  histories 
of  which  are  written 
astronomical  an- 


Fine  comets. 


3: 


in 


FIG.  127.— HOLMES'S  COMET. 


nals,  that  it   would 
be  a  hopeless  task 

to  enumerate  the  thousands  of  interesting  details  about 

them.     We  pay  brief  attention  to  a  few. 

The  great  comet  which  appeared  in  September,  1882, 


Comets  and  Meteors.  283 

was  the  most  magnificent  one  of  recent  years.  It  was 
bright  enough  to  be  visible  in  full  daylight,  close  to 
the  sun.  On  September  17  it  passed  across  the  sun, 
coming  within  300,000  miles  of  the  photosphere. 
Though  it  thus  dashed  directly  through  the  corona, 
and  may  indeed  have  encountered  some  of  the  solar 
prominences,  its  speed  was  unabated.  But  the  intense 
heat  to  which  it  was  exposed,  together  with  the  strain 
caused  by  the  tidal  action  of  the  sun,  apparently  dis- 
rupted the  nucleus.  In  less  than  a  month  it  exhibited 
two  centers  of  condensation.  As  the  days  rolled  by  still 
further  changes  took  place,  until  the  nucleus  had  be- 
come 50,000  miles  long,  and  was  ornamented  by  a 
number  of  centers  of  condensation,  the  largest  of  which 
was  5,000  miles  in  diameter. 

The  tail,  at  its  best,  was  100,000,000  miles  in  length,    , 

Filmy  d6bns. 

and  stretched  across  the  sky  as  a  splendid  golden  bar. 
Along  its  track  were  scattered  filmy  debris,  in  the  form 
of  companion  comets  six  or  more  in  number.  For 
nearly  two  months  there  projected  in  front  of  its  head  a 
luminous  sheath,  as  though  the  comet  were  a  sword 
which  was  being  thrust  into  its  scabbard. 

The  spectrum  was  very  bright,  and  indicated  the 
presence  of  hydro-carbons,  sodium,  and  iron  ;  calcium 
and  manganese  were  also  suspected.  The  comet  was 
not  lost  to  view  till  it  had  reached  a  distance  of  nearly 
500,000,000  miles  from  the  sun.  Its  orbit  is  a  very 
elongated  ellipse,  and  it  is  expected  to  return  in  the 
middle  of  the  twenty-seventh  century. 

Encke's  comet  was  discovered  in  1786,  and  was  found  Encke>s  comet, 
to  be  making  its  round  trip  in  only  three  years  and  a 
quarter,  the  shortest  known  cometic  period  of  revolution. 
It  is  insignificant  in  appearance,  but  made  trouble  for 
astronomers  as  soon  as  they  had  obtained  a  fair  grip 


284 


A  Study  of  the  Sky. 


Biela's  comet. 


Twins. 


A  meteoric 
shower. 


on  it.  No  matter  how  carefully  they  predicted  its 
successive  returns,  it  always  outran  the  figures,  and 
arrived  at  perihelion  ahead  of  time.  Such  an  effect 
would  be  produced  by  encounter  with  meteoric  bodies, 
which  offered  a  resistance  to  its  motion.  For  a  body 
which  is  retarded  loses  "centrifugal  force,"  and  is  con- 
sequently pulled  nearer  to  the  sun,  and  compelled  to 
describe  a  smaller  orbit,  in  which  it  goes  more  rapidly 
than  before.  Should  the  resistance  continue,  Encke's 
comet  must  inevitably  be  drawn  into  the  fiery  embrace 
of  the  sun. 

Biela's  comet  was  discovered  in  1826,  and  was  soon 
proven  to  be  one  of  short  period  ;  it  should  come 
around  once  in  six  and  three  fourths  years.  In  1832 
this  harmless  object  gave  rise  to  a  comet-scare  ;  for  the 
fact  became  noised  abroad  that  it  crossed  the  path  of  the 
earth,  and  people  jumped  to  the  conclusion  that  there 
would  be  a  collision.  But  when  the  comet  crossed  the 
earth's  orbit  our  planet  was  many  millions  of  miles  away. 

Thirteen  years  afterward  the  comet  split  in  twain, 
under  the  very  eyes  of  the  watchers.  The  operation 
occupied  several  days,  and  after  the  parts  had  separated 
to  a  distance  of  nearly  150,000  miles,  tails  were  shot 
out,  and  nuclei  blazed  up  in  rivalry.  The  original 
comet  had  possessed  neither  of  these  marks  of  cometic 
blue  blood.  They  interchanged  cometary  compliments 
by  alternately  brightening  and  fading  out.  In  1852 
they  were  seen  again,  the  distance  between  them  being 
then  ten  times  as  great  as  before.  They  were  still  ex- 
changing compliments,  and  thus  politely  bowed  them- 
selves out ;  for  they  have  never  been  seen  since. 

On  November  27,  1872,  the  earth,  when  crossing  the 
orbit  of  the  missing  comet,  encountered  a  fine  meteoric 
shower.  The  comet  should  have  been  millions  of  miles 


FIG.  128.— PHOTOGRAPH  OF  RORDAME'S  COMET,  SHOWING  MASSES  OF  MATTER  DRIVEN 

OFF  INTO  THE  TAIL. 
The  motion  of  the  comet  causes  the  stars  to  appear  as  streaks  on  the  negative. 


286 


A  Study  of  the  Sky. 


Lex  ell's  comet. 


Supposed 
returns. 


beyond  on  that  date.  Perhaps  the  earth  did  not  dash 
into  the  comet,  but  into  a  mass  of  meteoric  matter 
which  was  following  in  its  wake.  In  1885  there  was 
another  shower,  and  again  in  1892  ;  these  were  proba- 
bly due  to  the  same  group  of  bodies.  Either  the  comet 
has  become  invisible,  or  has  met  with  some  accident, 
which  has  disintegrated  it. 

Lexell's  comet  is  perhaps  the  most  tantalizing  one 
with  which  astronomers  have  had  to  deal.  It  was  first 
seen  in  1770,  and  Lexell  found  that  it  was  moving  in  an 
elliptical  orbit,  with  a  period  of  five  and  one  half  years. 
It  did  not  reappear  in  1776,  but  the  earth  was  not  then 
in  a  favorable  position  with  reference  to  it  and  the  sun. 
In  1781  circumstances  were  favorable,  but  the  comet 
was  a  truant.  Lexell  and  Laplace  investigated  the 
matter,  and  detected  Jupiter  in  the  role  of  mischief- 
maker.  Before  1767  the  comet  had  come  so  near  this 
planet  that  its  previous  orbit  had  been  transformed  in 
the  five  and  a  half  years  ellipse.  In  1779  it  came 
altogether  too  near  to  Jupiter,  and  was  tangled  up 
among  his  moons  ;  the  moons  moved  on  with  their 
accustomed  serenity,  but  the  comet's  orbit  was  so 
altered  that  it  was  given  up  for  lost.  But  in  1843  a 
comet  appeared  whose  orbit  was  somewhat  similar  to 
that  of  the  long-lost  Lexell.  Leverrier  went  to  the 
bottom  of  the  question,  and  decided  against  their  iden- 
tity. 

In  1889  Mr.  W.  R.  Brooks*  found  a  comet  which  has 
already  been  mentioned  as  accompanied  by  four  com- 
panions. It  too  had  been  troubled  by  Jupiter,  and  had 
skirmished  with  his  moons.  Surely  this  was  the  re- 
turned prodigal  ;  but  months  of  tedious  calculation  ren- 
dered its  identity  with  Lexell's  doubtful.  Six  more 

*  Of  Geneva,  N.  Y.  ;  director  of  the  Smith  Observatory. 


Comets  and  Meteors. 


287 


years  rolled  by,  and  in  August,  1895,  Dr.  Swift*  picked 
up  a  comet  which  proved  to  be  a  claimant  for  Lex  ell's 
vacant  chair.     A  European  astronomer  has  made  what  A  crucial  test, 
he  considers  to  be  a  crucial  test  of  the  matter,  and  an- 
nounces that  Lexell  is  found  at  last. 


FIG.  129.— COMET  c,  1893  (BROOKS). 

The  designation  of  this  comet  indicates  that  it  was  the 
third  one  discovered  in  1893.     The  first  one  discovered   (Brooks), 
in  a  given  year  is  called  comet  a,  the  second  comet  b, 
etc.     When  this  comet  was  first  seen  it  had  two  tails. 
The  main  tail  was  beautifully  symmetrical.     Four  years 


*  Director  of  the  Lowe  Observatory,  Echo  Mountain,  Cal. 


288 


A  Study  of  the  Sky. 


Space  not 
empty. 


The  air  is  a 
target. 


afterward  its  beauty  was  gone.  It  was  bent  and 
shattered.  The  subsidiary  tail  was  no  more,  and  the 
principal  tail  was  full  of  knotty  masses  of  nebulosity. 
The  appearance  suggested  that  the  comet  had  en- 
countered some  resisting  medium,  which  had  struck  its 
tail  near  the  middle,  and  bent  it.  The  comet  itself  was 
considerably  brighter.  The  strange  appearance  of  the 
tail  may  have  been  due  to  some  other  cause,  for  comets 
are  noted  for  trickiness. 

SHOOTING   STARS. 

We  are  accustomed  to  think  of  space  as  empty,  ex- 
cept where  here  and  there  a  massive  sun,  or  an  obedient 
planet,  or  perchance  an  erratic  comet  pursues  its  lonely 
way.  But  the  case  is  far  otherwise.  Innumerable 
small  bodies  traverse  that  part  of  space  in  which  the 
solar  system  is  now,  in  every  direction.  They  are  dark 
and  cold.  Those  in  our  neighborhood  are  revolving 
about  the  sun,  which  is  as  careful  to  enforce  obedience 
upon  these  specks  of  matter  as  upon  the  planets  them- 
selves ;  each  has  its  own  curve,  and  obeys  the  law  of 
gravitation. 

When  one  of  them  collides  with  the  earth  a  shooting 
star  is  produced.  The  shooting  star  does  not  strike  the 
earth's  surface,  but  impinges  upon  its  atmosphere.  So 
swift  is  its  motion  that  it  flames  into  incandescence 
when  it  encounters  the  higher  strata  of  the  air,  just 
as  a  cannon  ball  is  heated  when  it  strikes  a  target. 
If  the  shooting  star  is  coming  directly  toward  the  ob- 
server, so  that  he  looks  endwise  at  its  path,  it  is  simply 
a  bright  spot  which  flashes  out  for  an  instant.  The  vast 
majority  of  meteors  dart  at  one  side  of  the  observer,  and 
traverse  long  paths  across  the  heavens.  One  can  hardly 
look  at  the  sky  for  fifteen  minutes,  on  a  clear  moon- 


Comets  and  Meteors.  289 

less  night,  without  seeing  at  least  one  of  these  bodies. 
If  two  men  in  neighboring  towns  watch  meteors  for  an 

...  .  Observations 

hour  or  two,  and  each  marks  on  a  star  map  the  apparent  for  distance. 
path  of  every  one  which  he  sees,  noting  also  the  time  at 
which  he  observes  it,  the  height  of  any  meteor  which 
both  have  observed  may  be  calculated.  For  the  ap- 
parent path  as  seen  by  one  man  is  slightly  different  from 
that  seen  by  the  other,  and  if  the  distance  between  the 
observers  is  known,  the  distances  of  the  meteor  from 
each  of  them  at  the  instants  of  its  appearance  and  disap- 
pearance can  be  found  by  a  simple  calculation.  In  this 
way  the  average  height  of  a  shooting  star  has  been 
found  to  be  seventy-five  miles  when  it  is  first  seen,  and 
fifty  miles  when  it  disappears.  Their  visible  paths  are 
forty  or  fifty  miles  long  ;  their  average  velocity  is 
twenty-five  miles  per  second. 

Estimates  of  their  sizes  and  weights  are  obtained  from 
the  amount  of  light  which  they  emit.  One  which  rivals  ^eteors. 
Venus  at  its  best  may  weigh  from  fifty  to  one  hundred 
grains.  Faint  ones  weigh  less  than  a  grain  ;  many  of 
them  may  be  likened  to  grains  of  sand  or  canary  seeds. 
One  observer  sees  only  a  very  small  fraction  of  the  total 
number  which  bombard,  the  earth  daily  ;  he  can  ordi- 
narily see  from  four  to  eight  an  hour.  If  a  sufficient 
number  of  observers  were  distributed  uniformly  over  the 
entire  earth  they  would  see  from  one  to  two  millions 
every  two  hours. 

When  a  great  meteoric  shower  comes,  the  sky  is 
veined  with  thousands  of  luminous  paths  ;  all  of  them  The  radiant, 
prolonged  backward  meet  in  a  certain  place,  which  is 
called  the  radiant.  It  must  not  be  supposed  that  the 
meteors  emanate  from  this  point,  and  diverge  as  they 
come  on.  The  little  bodies,  which  have  joined  in  so 
bootless  a  fusillade  against  the  earth,  are  really  traveling 


2QO 


A  Study  of  the  Sky. 


Definite  times 
for  showers. 


in  parallel  paths,  like  the  drops  in  a  rain  storm.  One 
who  looks  out  of  the  rear  door  of  a  passenger  train 
notices  that  the  rails  appear  to  converge  in  the  distance. 
In  the  same  manner  the  parallel  meteoric  paths  seem  to 
converge  to  the  distant  radiant.  If  the  radiant  of  a 
shower  is  in  the  constellation  Andromeda,  the  meteors 
are  called  Andromedes  ;  if  in  Perseus,  Perseids,  etc. 

One  bright  shower  is  expected  within  a  day  or  two  of 
November  13  each  year.  The  reason  for  this  will  ap- 
pear from  a  simple  illustration.  Suppose  that  a  man 
walks  round  and  round  a  circular  grass  plot  upon  which 
a  spray  of  water  is  being  thrown  from  without.  Just  as 


A  meteoric 
river. 


The  August 
meteors. 


FIG.  130.— A  BESPRINKLING. 

often  as  he  passes  the  spot  where  the  stream  of  water 
plays  he  is  besprinkled.  Replace  the  man  by  the  earth, 
and  the  stream  of  water  by  a  mighty  river  of  meteoric 
matter,  which  persistently  flows  by  a  certain  spot  in  the 
earth's  orbit.  Whenever  the  earth  passes  by  that  spot, 
as  it  does  at  a  given  time  every  year,  it  is  besprayed 
with  meteors. 

The  meteoric  river  does  not  have  a  source  and  a 
mouth  as  terrestrial  rivers  have.  Its  source  and  mouth 
are  united,  the  entire  stream  being  a  vast  ellipse  within 
which  the  sun  lies.  In  some  parts  of  the  stream  the 
meteors  are  more  thickly  crowded  together  than  in 
others.  Whenever  the  earth  dashes  into  a  dense  por- 
tion, the  shower  is  unusually  magnificent.  A  stream  is 


Comets  and  Meteors.  291 

broader  in  some  places  than  in  others  ;  when  the  earth 
plunges  into  a  broad  portion  the  shower  may  begin  be- 
fore its  usual  time.  The  meteors  in  some  streams  are 
mostly  massed  in  a  vast  shoal,  instead  of  being  distrib- 
uted around  the  orbit. 

The  August  meteors  are  most  numerous  about  the 
tenth  of  the  month  ;  but  the  meteoric  river  is  so 
broad  that  the  earth  takes  over  a  month  to  go  through 
it.  Night  after  night,  from  July  18  to  August  22,  some 
meteors  belonging  to  this  aggregation  may  be  observed. 
Their  radiant  is  in  Perseus.  There  are  occasional  gaps 
in  the  stream,  so  that  some  years  bring  no  August  dis- 
play worthy  of  the  name  of  a  shower.  The  elliptical 
orbit  in  which  the  meteors  move  extends  beyond  Nep- 
tune, and  the  stream  requires  over  one  hundred  years 
for  a  single  revolution. 

The  shower  of  November  13  emanates  from  the  con- 

.  ,  T          The  shower  of 

stellation  Leo  ;  the  meteors  are  therefore  known  as  Le-   November  13. 

onids.     Generally  the  display  is  not  at  all  brilliant  ;  but 

once  in  thirty-three  years  it  is  of  wonderful  splendor. 

The  first  recorded  appearance  of  this  shower  was  in  902 

A.  D. ,  which  was  long  known  as  ' '  the  year  of  the  stars." 

For  during  the  night  in  which  the  ancient  Sicilian  city 

of  Taormina  was  captured  by  the  Saracens,  men  saw 

' '  as  it  were,  lances,  an  infinite  number  of  stars,  which 

scattered  themselves  like  rain  to  right  and  left. ' ' 

An  imaginative  Portuguese  chronicler  relates  that  in 
the  year  1366,  "  three  months  before  the  death  of  the  of  1366. 
king  Dom  Pedro,  there  was  in  the  heavens  a  move'ment 
of  stars  such  as  man  never  before  saw  or  heard  of.  At 
midnight  and  for  some  time  after,  all  the  stars  moved 
from  the  east  to  the  west,  and  after  being  collected  to- 
gether, they  began  to  move,  some  in  one  direction  and 
others  in  another.  And  afterward  they  fell  from  the 


292 


A  Study  of  the  Sky. 


The  display 
of  1833. 


Another  No- 
vember shower. 


sky  in  such  numbers,  and  so  thickly  together,  that  as 
they  descended  low  in  the  air,  they  seemed  large  and 
fiery,  and  the  sky  and  the  air  seemed  to  be  in  flames, 
and  even  the  earth  appeared  as  if  ready  to  take  fire." 

On  November  12,  1833,  the  falling  stars  were  as  thick 
as  snowflakes  ;  many  were  brighter  than  Venus.  The 
negroes  in  the  Southern  States  were  struck  with  terror, 
believing  that  the  end  of  the  world  was  at  hand.  They 
groaned,  wept,  prayed,  and  rolled  on  the  earth  in 
ecstasies  of  terror. 

The  year  1866  brought  another  fine  shower.  The 
next  date  on  the  program  is  1899.  The  length  of  the 
dense  part  of  the  meteoric  stream  is  2,000,000,000 
miles,  and  it  occupies  nearly  two  years  in  passing  any 
given  point.  The  year  1898  may  therefore  furnish  a 
fine  shower.  The  periodic  time  of  this  shower  is  33^ 
years.  The  direction  from  which  the  meteors  come 
is  nearly  opposite  to  that  in  which  the  earth  moves  : 
they  travel  at  the  rate  of  twenty-six  miles  a  second, 
while  the  earth  has  a  velocity  of  eighteen  miles  a 
second.  The  effect  is  the  same  as  if  the  earth  were  at 
rest,  and  the  meteors  hurled  themselves  against  it  with  a 
velocity  of  forty-four  miles  a  second.  Such  missiles, 
if  not  checked  by  the  air,  would  go  from  New  York  to 
Chicago  in  twenty  seconds.  It  is  not  astonishing  that 
the  meteors  are  bright  and  leave  vivid  trails  behind 
them. 

In  the  latter  part  of  November  comes  another  shower, 
the  radiant  of  which  is  in  the  constellation  of  An- 
dromeda. The  meteors  pursue  the  earth  and  overtake 
it ;  because  of  this  they  do  not  rush  into  the  air  with  the 
impetuosity  which  characterizes  the  Leonids.  Their 
trains  are  short  and  of  a  reddish  hue.  In  1872  some  of 
them  looked  as  large  as  the  moon  ;  in  1885  and  1892 


Comets  and  Meteors. 


293 


there  were  fine  showers  ;  another  is  expected  in  1898  or 
1899.     This  shower  derives  special  interest  from  its  sup- 
posed connection  with  Biela's  comet.    The  meteors  pur-   connection 
sue  the  same  orbit  as  the  lost  comet,  and  it  is  possible  Smet.le ' 
that  they  are  the  products  of  its  disintegration.     During 


^  vv 


The  Mazapil 


FIG.  131.— PHOTOGRAPH  SHOWING  A  METEOR'S  PATH  AMONG 
THE  STARS. 

the  1885  shower  there  fell  at  the  town  of  Mazapil  in 
Mexico  a  piece  of  meteoric  iron,  which  may  have  been  a  meteorite, 
piece  of  the  comet.  In  1892  the  meteors  came  on 
November  23,  instead  of  November  27,  the  date  usually 
assigned  ;  this  was  due  to  a  disturbance  of  the  meteoric 
orbit  caused  by  the  attraction  of  Jupiter. 


294 


A  Study  of  the  Sky. 


Relation  be- 
tween comets 
and  meteors. 


There  are  other  instances  of  a  connection  between  a 
meteor-shower  and  a  comet.  The  orbit  of  the  August 
meteors  is  identical  with  that  of  the  bright  comet  of 
1862.  The  great  thirty-three  year  shower  of  Leonids 
follows  hotly  on  the  trail  of  Tempel's  comet. 

The  relation  between  comets  and  meteors  is  therefore 
intimate.  A  comet  is  a  group  of  small  bodies  somewhat 
compacted  ;  a  meteoric  shower  is  caused  by  a  group  of 
small  bodies  more  widely  separated.  The  change  which 
took  place  in  the  nucleus  of  the  great  comet  of  1882  is 
one  of  many  instances  of  the  disruptive  power  which  the 
sun  exercises  upon  comets  ;  its  tidal  action  upon  them 
tends  to  scatter  the  bodies  of  which  they  are  composed. 
These  bodies  when  scattered  cause  a  meteoric  shower, 
if  they  collide  with  the  earth. 

Akin  to  meteors  and  comets  is  the  zodiacal  light, 
which  is  a  hazy  white  beam  of  light,  best  seen  early  on 
a  spring  evening.  Resting  on  the  western  horizon  it 
slants  upward  toward  the  south.  In  the  tropics  it  is 
seen  as  a  light  girdle  encircling  the  sky.  It  lies  in  the 
zodiac  and  is  surmised  to  be  an  envelope  of  meteors 
surrounding  the  sun,  after  the  fashion  of  a  huge  lens. 

METEORITES. 


The  term  meteors  includes  both  shooting  stars,  which 

Appearance  of  a  .  »*••«_   /i 

flying  fire-ball,  we  have  already  considered,  and  meteorites.  I  he  latter 
are  bodies  of  such  size  and  toughness  that  they  can 
pierce  the  earth's  atmosphere  and  find  a  resting  place 
upon  its  surface.  The  flight  of  a  large  meteorite  is  sig- 
nalized by  striking  phenomena.  If  it  come  in  the  night 
time,  it  is  a  splendid  fire-ball  followed  by  a  flaming 
train  ;  there  is  a  roar  like  that  of  the  sea  in  a  storm,  ac- 
centuated by  occasional  detonations.  In  a  few  seconds 
there  remains  only  a  luminous  streak  of  glowing  ma- 


The  zodiacal 
light. 


Comets  and  Meteors.  295 

terial,  which  has  been  wiped  off  from  the  exterior  of  the 
meteorite,  as  it  dashed  through  the  aerial  furnace. 

The    intensity    of    the    heat   which    a    meteorite    ex-   Atremendout 
periences  may  be  imagined  from  the   appearance  of  a   fire-ball, 
fire-ball  which  was  seen  in  England  in  1869.     The  fiery 
envelope  which  enswathed  it  was  more  than  four  miles 
in  diameter,  and  the  entire  body  was  consumed  in  five 
seconds.     A  cloud  of  glowing  vapor  fifty  miles  long  was 
visible  for  nearly  an  hour. 

Sometimes  a  meteorite  traverses  a  course  hundreds  of 
miles  in  length  before  the  steady  pressure  of  the  air 
triumphs  and  brings  it  to  the  earth.  Usually  it  breaks 
into  numerous  fragments  while  flying,  and  descends  as  a 
shower  of  stony  missiles. 

The  fragments  do  not  penetrate  the  earth  as  deeply   Destructive 
as  would  a  projectile  hot  from  the  mouth  of  a  rifled  gun.    P°wers- 
Still  their  destructive  powers  are  by  no  means  to  be  de- 
spised, for  they  have  been  known  to  kill  men  and  to  de- 
stroy buildings.     Very  few  such  catastrophes  have  been 
recorded,  because  buildings  and  men  cover  a  very  small 
part  of  the  earth,  and  meteorites  are  infrequent  visitors. 

Meteorites  have  been  known  to  come  to   earth   so  Coated  with 
quickly  that  the  heat  to  which  they  were  exposed  had  ice- 
not  time  to  penetrate  their  interiors.     A  meteoritic  frag- 
ment,  which  once  embedded  itself  in  a  moist  spot  of 
ground  in  India,  was  found  half  an  hour  afterward  coated 
with  ice. 

The  appearance  of  a  fallen  meteorite  testifies  loudly  to   Appearanceofa 
the  experience  which  it  has  passed  through.     Most  of  fallen  meteorite, 
these  objects  are  stones  which  have   thin  crusts    pro- 
duced by  the  fusion  of  their  surfaces.    In  case  a  meteor- 
ite bursts  just  before  it  is  brought  to  rest,   the  freshly 
cracked  surfaces,    having  been    exposed  to  very  little 
heat,  preserve  their  roughness,    and  may  be  fitted  to- 


296 


A  Study  of  the  Sky. 


Their  compo- 
sition. 


Old  records. 


A  rare  tract. 


gether  again.  Some  parts  of  the  stony  masses  are  often 
softer  than  others,  and  are  quickly  fused  and  swept  away 
into  the  meteoric  train.  The  captured  meteorite  is  then 
pock-marked  with  numerous  pits. 

In  all  large  collections  of  these  bodies  are  a  few  com- 
posed of  iron  alloyed  with  nickel  ;  some  of  them  are 
very  formidable  projectiles  weighing  several  tons. 
Stony  meteorites  often  have  bits  of  iron  scattered 
through  them  ;  iron  meteorites  frequently  have  pockets 
laden  with  stone.  These  combinations  are  not  limited  to 
meteorites,  but  are  also  found  in  such  basaltic  rocks  as 
those  of  the  Giants'  Causeway. 

Chemical  analyses  of  meteorites  have  brought  to  light 
no  new  element ;  twenty-five  elements  have  been  found, 
most  of  which  are  common  on  the  earth  ;  the  precious 
metals  have  not  been  discovered.  Meteoric  stones  are 
composed  of  minerals,  which  are  abundant  in  terrestrial 
rocks  of  volcanic  origin. 

In  1891  some  300  fragments  of  meteoric  iron  were 
found  in  the  Canon  Diablo  in  Arizona  ;  minute  diamonds 
were  embedded  in  them.* 

There  are  hundreds  of  accounts  of  falls  of  meteorites 
during  the  past  2,500  years.  The  Greeks  and  Romans 
considered  them  as  celestial  omens,  and  kept  some  of 
them  in  temples.  One  at  Mecca  is  adored  by  the 
faithful.  The  emperor  Jehangir  is  said  to  have  had  a 
sword  forged  from  a  meteorite,  which  fell  in  1620  in  the 
Punjab.  An  Ohio  Indian  mound  has  yielded  up  copper 
earrings  plated  with  meteoric  iron. 

We  subjoin  four  interesting  accounts  of  meteorites. 
The  first  is  taken  from  a  rare  tract  preserved  in  the 
British  Museum  ;  its  opening  sentences  are  : 


*  The  diamonds  were  used  at  Tiffany's  pavilion  in  the  World's   Fair  at 
Chicago  for  polishing  other  diamonds. 


Comets  and  Meteors.  297 

So  Benummed  we  are  in  our  Senses,  that  albeit  God  him- 
selfe  Holla  in  our  Eares,  wee  by  our  Wills  are  loath  to  heere    Heedlessness. 
him.     His  dreadfull  Pursiuants  of  Thunder  and  Lightning  ter- 
rifie  vs  so  long  as  they  have  vs  in  their  fingers,  but  beeing  off, 
we  dance  and  sing  in  the  midst  of  our  Follies.* 

After  moralizing  at  some  length  the  author   narrates 
the  event  which  has  inspired  his  pen  : 

The  name  of  the  Towne  is  Hatford,  some  eight  miles  from 
Oxford.  Upon  Wensday,  being  the  ninth  of  this  instant 
Moneth  of  April  1628,  about  five  of  the  clocke  in  the  afternoone 
this  miraculous  prodigious  and  fearefull  handy-worke  of  God 
was  presented.  ...  It  beganne  thus  :  First  for  an  onset 
went  off  one  great  Cannon  as  it  were  of  thunder  alone,  like  a 
warning  peece  to  the  rest  that  were  to  follow.  Then  a  little 
while  after  was  heard  a  second  :  and  so  by  degrees  a  third,  on- 
till  the  number  of  20  were  discharged  (or  there-abouts)  in  very 
good  order,  though  in  very  great  terror.  In  some  little  dis- 
tance of  time  after  this  was  audibly  heard  the  sound  of  a  Drum 
beating  a  Retreate.  Amongst  all  these  angry  peales  shot  off 
from  Heauen  this  began  a  wonderful  admiration,  that  at  the 
end  of  the  report  of  euery  cracke,  or  Cannon-thundering,  a 
hizzing  Noyse  made  way  through  the  ayre,  not  unlike  the  fly-  A  "  hizzing 
ing  of  Bullets  from  the  mouthes  of  great  Ordnance  :  and  by  Noyse- 
the  judgment  of  all  the  terror-stricken  witnesses  they  were 
Thunderbolts.  For  one  of  them  was  scene  by  many  people  to 
fall  at  a  place  called  Bawlkin  Greene,  being  a  mile  and  a  half 
from  Hatford  :  Which  Thunderbolt  was  by  one  Mistris  Greene 
caused  to  be  digged  out  of  the  ground,  she  being  an  eye-wit- 
nesse  amongst  many  others  of  the  manner  of  the  falling.  The 
form  of  the  Stone  is  three-square,  and  picked  in  the  end.  In 
colour  outwardly  blackish,  somewhat  like  iron  :  crusted  over 
with  that  blacknesse  about  the  thicknesse  of  a  shilling.  Within 
it  is  a  soft,  of  a  grey  colour,  mixed  with  some  kind  of  minerall, 
shining  like  small  peeces  of  glasse. 

A  detonating  fire-ball,  no  fragments  of  which  came  to   A  detonatin 
the  ground,  was  seen  on   December  21,   1876.      From   fire-bail, 
some  point  in  Kansas  it  sped  to  Niagara  Falls,  travel- 


*  See  Lockyer's  "  Meteoritic  Hypothesis,"  pages  5-7. 


FIG.  132. — A  METEORITE  SEEN  JULY  27,  1894. 


Comets  and  Meteors.  299 

ing  at  the  rate  of  ten  miles  or  more  a  second.  When 
passing  over  Illinois  it  exploded,  and  formed  a  cluster  of 
fire-balls  which  occupied  a  space  forty  miles  long  and 
five  miles  broad.  v  Several  minutes  after  the  inhabitants 
of  Bloomington  saw  the  stream  of  fire-balls  coursing 
past  overhead,  they  were  startled  by  a  thunder-peal, 
which  fairly  shook  the  town,  and  led  some  to  believe 
that  a  miniature  earthquake  was  in  progress.  Sound 
travels  a  mile  in  five  Seconds,  and  the  explosion  was 
heard  in  Bloomington  fifteen  minutes  after  the  disrup- 
tion of  the  meteor  occurred.  The  sound  of  the  ex- 
plosion must  have  traveled  180  miles  before  it  smote 
upon  the  ears  of  the  people  of  Bloomington.  Had  the 
fiery  visitor  come  within  eighteen  miles  of  Bloomington 
instead  of  180,  how  appalling  the  thunderings,  which 
would  have  been  multiplied  a  hundred  fold  !  Fortu- 
nately it  was  at  an  altitude  of  seventy-five  miles  when  it 
was  first  seen,  and  kept  at  a  great  height,  finally 
escaping  from  the  air  after  it  had  passed  Niagara  Falls. 
Brenham  township,  Kiowa  County,  Kansas,  was 
visited  by  a  shower  of  meteoric  iron  at  some  time  be-  An  iron  hail, 
fore  white  men  had  established  themselves  there.  From 
time  to  time  the  early  settlers  plowed  up  these  curious 
pieces  of  iron.  Though  the  people  called  the  strange 
masses  meteors,  they  did  not  realize  their  pecuniary 
value.  A  cowboy,  however,  attempted  to  carry  some 
off,  but  his  pony  was  unequal  to  the  task.  He  therefore 
buried  them,  expecting  to  return  at  some  future  time  ; 
but  death  frustrated  his  plan.  A  good  woman,  who 
was  unable  to  persuade  her  relatives  of  the  value  of 
these  chunks  of  iron,  finally  took  matters  into  her  own 
hands,  sent  for  a  college  professor,  sold  her  meteors, 
and  paid  off  the  mortgage  on  the  farm  from  the  pro- 
ceeds. 


300  A  Study  of  the  Sky. 

On  February  10,  1896,  a  fire-ball  exploded  over  the 
fire-baifdrid  c^  °*  Madrid»  in  tne  middle  of  the  forenoon.  The 
sun  was  shining  brightly,  so  that  the  celestial  visitor 
was  seen  only  as  a  swiftly  moving  cloud.  There  was  a 
loud  report,  which  caused  a  panic  in  schools  and  facto- 
ries, and  thus  led  to  the  injury  of  several  people.  Many 
windows  were  shattered,  and  a  partition  wall  in  a  build- 
ing occupied  by  the  United  States  legation  collapsed.  * 

*  So  said  the  newspapers. 


CHAPTER  XVII. 

/  •' 

THE    FIXED    STARS. 

"  Ye  stars  !  bright  legions  that,  before  all  time, 
Camped  on  yon  plain  of  sapphire,  who  shall  tell 
Your  burning  myriads,  but  the  eye  of  Him 
Who  bade  through  heaven  your  golden  chariots  wheel  ?" 

—  Croly. 

THE  number  of  stars  visible  to  an  average  eye  on  a 
good  night  is  not  far  from  2,000.  Near  the  horizon 
faint  stars  are  blotted  out  by  atmospheric  vapors.  If 
we  could  see  all  the  stars  on  the  celestial  sphere  as  well 
as  we  see  those  near  the  zenith,  6,000  would  be  visible 
without  optical  aid.  A  spy-glass  brings  out  thousands 
otherwise  unseen.  By  the  largest  telescopes  millions 
are  revealed ;  hundreds  of  millions  are  sufficiently  bright 
to  record  themselves  on  photographic  plates. 

The  Milky  Way  or  Galaxy  has  been  previously  de-  The  Galaxy 
scribed  as  the  beautiful  river  of  light  which  flows  across 
the  sky,  embracing  a  countless  host  of  faint  stars.  One 
of  the  most  interesting  parts  of  it  is  in  the  south,  when 
the  summer  twilight  has  faded.  The  Galaxy  there  di- 
vides for  a  portion  of  its  length  into  two  roughly  parallel 
streams,  and  glows  in  places,  as  if  illuminated  by  cos- 
mical  fires. 

A  marvelous  complexity  of  structure  is  brought  out  by   complexity 
photographic  plates  exposed  for  several  hours.     There  ofstructure- 
are  curious  curved  lines  of  stars,  vast  cloud-like  forms, 
long  narrow  lanes,  and  dark  spots  of  various  shapes. 

Tree-like  forms,  similar  to  those  of  some  solar  promi- 
301 


302 


A  Study  of  the  Sky. 


Tree-like  forms. 


WEST. 


EAST. 


Distribution  in 
the  sky. 


nences,  are  of  not  infrequent  occurrence  ;  some  of  them 
are  dark,  and  some  bright.  They  have  been  supposed  to 
be  analogous  to  solar  prominences,  not  only  in  form, 
but  also  in  origin.  According  to  this  view  they  are  due 

to  stupendous 
uprushes  into  a 
resisting  medium. 
The  dark  forms 
may  be  caused 
by  an  absence  of 
matter,  or  by  the 
presence  of  vast 
masses  of  absorb- 
ing  material, 
which  obscure 
the  stars  lying 
beyond  them. 

Naked-eye 
stars  are  distrib- 
uted over  the 
entire  celestial 
sphere  with  con- 
siderable  uni- 
formity, but 
those  which  are 
invisible  without 
telescopic  aid  are 
arranged  very 
differently.  They 
are  most  thickly  crowded  in  the  Milky  Way.  On  either 
side  of  it  the  number  in  a  given  area  is  less.  The  further 
one  goes  away  from  the  Galaxy,  the  fewer  the  tele- 
scopic stars  are.  If  we  call  the  Milky  Way  the  galactic 
equator  of  the  celestial  sphere,  a  given  area  in  it  con- 


FIG.  133.— OUTLINES  OF  DARK  STRUCTURES 
IN  THE  GALAXY. 


The  Fixed  Stars.  303 


tains  on  the  average  thirty  times  as  many  stars  as  an 
equal  area  at  either  galactic  pole. 

We  have  already  learned  how  the  stars  are  divided 
into  constellations,  how  they  are  named,  how  their  bright- 
ness  is  estimated  in  magnitudes,  and  how  catalogues  of 
them  are  made.  The  greatest  of  all  star  catalogues  is 
now  being  formed  by  the  aid  of  photography.  A  num- 
ber of  observers  scattered  over  the  world  have  united  to 
photograph  the  entire  heavens,  using  instruments  of  the 
same  size  and  construction,  and  after  the  photographs 
have  been  taken  several  years  will  be  required  to  meas- 
ure them  and  to  prepare  the  results  for  publication. 

Astronomers  are  far  from  being  content  with  making 
catalogues  or  maps  of  the  stars.  They  wish  to  know 
how  far  they  are  away,  what  their  dimensions  are,  of 
what  substances  they  are  composed,  how  they  change 
appearance,  how  they  move,  what  relation  they  bear  to 
our  sun,  and  what  their  origin  and  destiny  may  be.  Let 
us  take  a  glimpse  of  what  has  been  done  along  these 
lines. 

In  order  to  measure  the  distance  of  a  star  a  base  line 

Measurements 

of  known  length  must  be  available.  When  an  Atlantic  of  distance, 
liner  passes  by  a  lighthouse,  a  man  at  the  prow  sees  the 
lighthouse  in  a  direction  different  from  that  in  which  a 
man  at  the  stern  sees  it.  If  they  knew  the  length  of  the 
ship,  and  had  suitable  instruments  for  measuring  angles, 
they  could  find  the  distance  from  the  lighthouse  to 
either  one  of  them,  at  a  given  instant. 

If  two  astronomers,  one  in  northern  Russia,  the  other 
at  the  Cape  of  Good  Hope,  should  both  look  at  the 
moon  at  the  same  instant,  it  would  appear  to  them  to  lie 
in  slightly  different  directions,  and  they  could  calculate 
its  distance.  But  if  they  were  to  try  the  same  plan  with 
a  fixed  star  they  would  be  balked  because  no  instru-  , 


304 


A  Study  of  the  Sky. 


A  long  base 
line. 


ments  are  sufficiently  delicate  to  measure  the  very  slight 
difference  between  the  directions  in  which  the  two  men 
see  the  star.  A  longer  base  line  must  be  used  than  the 
distance  from  St.  Petersburg  to  the  Cape  of  Good  Hope. 
If  an  astronomer  measure  the  right  ascension  and  de- 
clination of  Sirius  on  January  i  and  again  on  July  i, 
when  the  earth  has  gone  half  way  around  its  orbit,  to  a 


The  nearest 
star. 


FIG.  134.— A  PART  OF  THE  MILKY  WAY  IN  CYGNUS. 

point  1 86,ooo,oC)0  miles  distant  from  its  former  position, 
he  will  find  that  Sirius  has  apparently  changed  its  posi- 
tion slightly,  on  account  of  the  observer's  change  of 
view-point.  With  the  aid  of  a  little  mathematics  the 
celestial  surveyor  computes  the  distance  to  Sirius. 

Most  of  the  stars  are  at  such  inconceivable  distances 


The  Fixed  Stars. 


that  even  the  base  line  of  186,000,000  miles  is  insuffi- 
cient. Our  nearest  neighbor,  so  far  as  present  knowl- 
edge goes,  is  Alpha  Centauri,  which  is  275,000  times  as 
far  away  as  the  sun  ;  its  distance  is  over  25,000,000,- 
000,000  miles.  Sirius  is  twice  as  far  away,  and  light 
takes  eight  years  to  come  from  it  to  us.  The  pole-star 
shines  by  light  which  left  it  fifty  years  ago. 

No  one  has  yet  been  able  to  measure  directly  the  The  sizes  of 
diameter  of  any  star,  on  account  of  their  amazing 
distances.  Though  the  sun's  diameter  is  860,000  miles, 
it  would  look  to  an  eye  near  Sirius  as  small  as  a 
marble  2,000  miles  away.  Yet  we  can  get  a  rough 
estimate  of  the  probable  size  of  a  star,  the  distance  of 
which  is  known,  by  measuring  the  amount  of  light 
which  it  emits.  Capella  and  Vega  are  thought  to  be 
much  larger  than  the  sun.  Some  are  so  bold  as  to 
estimate  that  Arcturus  is  1,000,000  times  as  large  as 
the  sun  ;  but  such  an  estimate  must  be  considered  very 
insecure.  When  two  stars  are  close  together  and  re- 
volve about  their  common  center  of  gravity,  the  swift- 
ness of  their  motion  combined  with  their  distances  from 
us  and  each  other  gives  a  clue  to  their  masses.  Periodic 
shif tings  of  the  lines  in  a  star's  spectrum  also  furnish 
evidence,  which  we  cannot  here  detail. 

Mizar  at  the  bend  of  the  handle  of  the  Great  Dipper 
is  thought  to  be  at  least  forty  times  as  massive  as  the 
sun.  Algol  is  periodically  eclipsed  by  a  dark  body 
revolving  about  it.  From  the  length  of  the  eclipse, 
combined  with  other  data  obtained  spectroscopically, 
a  diameter  of  1,000,000  miles  has  been  figured  out 
for  it. 

No  star  sends  us  a  measurable  amount  of  stellar  heat ; 
the  entire  body  of  stars  gives  one  sixtieth  as  much  light  S 
as  the  full  moon,  and  decidedly  mitigates  the  darkness 


3o6 


A  Study  of  the  Sky. 


Optical 
doubles. 


Physical 
doubles. 


Does  gravity 
bind  binaries? 


of  the  night.      Seven  billion  stars  like  Sirius  would  be 
required  to  make  night  as  bright  as  day  now  is. 

*  DOUBLE   STARS. 

Double  stars  exist  in  considerable  numbers,  10,000 
being  catalogued.  Many  more  have  been  seen,  but 
adjudged  to  be  too  faint  to  deserve  attention,  until  their 
brighter  brethren  have  been  investigated.  A  double 
star  appears  as  one  to  the  naked  eye,  but  is  split  up,  by 
telescopic  or  spectroscopic  aid,  into  two  stars. 

An  optical  double  is  one  the  components  of  which  are 
not  really  close  together;  one  of  the  two  components 
lies  far  beyond  the  other,  but  in  nearly  the  same  line  of 
sight. 

In  a  physical  double  star,  or  binary,  the  two  stars  are 
neighbors  subject  to  one  another's  attraction.  Each  of 
the  two  stars  revolves  about  their  common  center  of 
gravity.  Such  a  system  is  unlike  ours,  where  a  number 
of  comparatively  small  and  cool  bodies  revolve  about  a 
large  hot  body.  In  a  binary  system  there  are  two  suns, 
often  equal  in  size,  which  revolve  like  partners  in  a 
waltz.  Each  of  them  may  be  surrounded  by  a  troop  of 
planets  for  aught  we  know.  If  Jupiter  were  transported 
to  the  vicinity  of  Alpha  Centauri,  and  became  a  planetary 
attendant  upon  it,  the  largest  telescopes  would  seek  for 
it  in  vain. 

It  is  not  yet  known  that  the  force  of  gravitation, 
which  keeps  the  planets  in  their  orbits,  controls  the 
motion  of  binary  stars,  but  there  is  so  much  evidence  in 
favor  of  this  supposition  that  it  is  accepted  as  a  fact. 
Since  the  spectroscope  shows  that  the  stars  are  com- 
posed of  elements  found  on  the  earth  and  the  sun,  as 
well  as  in  other  planets,  comets,  and  meteors,  there  is 
no  good  reason  for  thinking  that  the  same  materials, 


The  Fixed  Siars.  307 


when  found  in  the  stars,  will  not  attract  each  other 
according  to  the  same  law  which  we  observe  in  the  solar 
system.  When  the  orbits  of  double  stars  are  computed 
upon  the  assumption  that  their  motion  is  due  to  the 
force  of  gravity,  and  when  their  relative  positions  are 
predicted  for  years  to  come,  the  predictions  are  verified 
by  the  motions  actually  observed.  A  mass  of  evidence 
is  continually  accumulating  to  show  that  physical, 
chemical,  and  mechanical  laws,  discovered  by  experi- 
mentation upon  terrestrial  bodies,  hold  good  throughout 
the  visible  universe. 

The  history  of  the  discovery  of  the  duplicity  of  Sirius  sirius 
strengthens  the  view  that  the  universe  is  a  wonderful 
unit,  subject  throughout  its  wide  extent  to  laws  which 
are  the  expression  of  the  will  of  its  Creator.  During  the 
first  half  of  the  nineteenth  century  thousands  of  accurate 
observations  of  the  right  ascension  and  declination  of 
Sirius  were  made.  The  more  earnestly  accuracy  was 
sought,  the  more  impossible  it  was  to  make  the  observa- 
tions agree  with  one  another.  It  became  evident  that 
Sirius  was  not  fixed  on  the  face  of  the  sky. 

More  than  half  a  century  ago  the  illustrious  German  A  curviiinear 
astronomer  Bessel  attacked  the  problem,  and  announced  motlon- 
that  Sirius  was  moving  in  a  tiny  curve,  and  that  this 
curvilinear  motion  was  probably  a  case  of  orbital  revolu- 
tion,  in  which  an  unknown  companion  took  part.      A   Acompani0n 
few    years   afterward   two   other   German    astronomers 
made  a  yet  more  thorough  discussion,  and  reached  the 
conclusion  that  the  companion  made  a  complete  revolu- 
tion in  fifty  years.     They  also  pointed  out  the  direction 
in  which  the  companion  then  lay  from  Sirius,  and  the 
direction  in  which  it  was  moving.      Eight  years  later 
their  confidence  was  rewarded  by  the  discovery  of  the 
disturbing  body  by  Alvan  G.  Clark,  who  was  not  aware 


308 


A  Study  of  the  Sky. 


Spectroscopic 
doubles. 


Shifting  of 
the  lines. 


of  the  prediction  made  by  the  two  Germans.  The  com- 
panion is  not  T^ijo^  as  bright  as  the  main  star,  but  it 
is  one  half  as  heavy.  It  is  therefore  a  much  cooler 
object  than  Sirius,  and  may  in  the  course  of  ages  be- 
come a  genuine  planet,  though  an  enormous  one. 

Perhaps  the  most  interesting  class  of  double  stars 
embraces  those  in  which  the  two  components  are  so 
close  together  that  they  can  never  be  separately  seen. 
Though  the  two  may  be  equal  in  size  and  brightness, 
they  look  like  one  perfectly  round  body,  no  matter  how 
high  the  magnifying  power  employed.  Their  existence 
becomes  known  through  the  spectroscope.  If  the 
bodies  are  just  alike,  each  of  them  gives  a  particular 


FarM 


FIG.  135. — MOTION  OF  THE  COMPONENTS  OF  A  DOUBLE  STAR. 

spectrum  ;  if  they  are  at  rest  the  two  spectra  coincide  ; 
but  if  they  are  in  motion  in  a  plane  turned  nearly  edge- 
wise to  us,  one  body  at  a  certain  point  in  its  orbit  is 
moving  away  from  us  quite  rapidly,  while  the  other  is 
approaching.  This  is  the  state  of  affairs  when  the 
bodies  are  at  A  and  B,  Fig.  135. 

The  lines  in  the  spectrum  of  one  body  are  therefore 
shifted  in  one  direction,  and  the  corresponding  lines  in 
the  other  spectrum  move  in  the  other  direction.  At  the 
instant  when  the  bodies  are  at  C  and  D  respectively 
neither  of  them  is  being  carried  by  its  orbital  revolution 
toward  the  earth  or  away  from  it.  The  spectral  lines  are 
therefore  not  shifted  by  the  orbital  revolution  at  that  time. 

When  the  stars  are  at  C  and  D  their  spectra  coincide; 
when  they  are  at  A  and  B  the  spectra  are  separated,  and 


The  Fixed  Stars.  309 


corresponding  lines,  which  formerly  coincided,  now 
stand  side  by  side.  In  a  word,  the  dark  lines  some- 
times appear  single  and  sometimes  double,  the  doubling 
recurring  at  regular  intervals. 

Spica,  in  Virgo,  is  a  rapid  spectroscopic  binary,  the 
revolution  being  completed  in  four  days.  If  the  com- 
ponents are  equal  they  are  but  6,000,000  miles  apart,  and 
each  is  a  third  heavier  than  the  sun. 

A  system  not  infrequently  contains  three  or  more  re-   _ 

3  .  Multiple  stars. 

volving  suns.  An  interesting  quadruple  system  is  found 
in  Epsilon  Lyrae,  one  of  the  faint  stars  near  Vega.  It 
has  already  been  described  under  the  constellation  Lyra. 
Theta  Orionis,  which  is  in  the  great  nebula  in  Orion,  is 
a  sextuple  star.  There  are  many  instances  of  multiple 
stars,  where  several  are  grouped  together.  Stars  in  a 
given  group  may  be  really  close  together,  so  as  to  form 
a  revolving  system,  or  they  may  be  like  optical  doubles, 
in  which  one  star  is  a  great  ways  beyond  the  other. 
Zeta  Cancri  is  composed  of  three  visible  stars,  two  of 
which  are  close  together  and  constitute  a  binary  system. 
The  third  star  seems  to  revolve  about  the  binary,  but  its 
motion  is  subject  to  irregularities,  thought  by  some  to 
be  due  to  an  invisible  member  of  the  system. 

STELLAR    SPECTRA. 

When  stars  are  examined  with  the  spectroscope,  great 
diversities  between  them  become  apparent.  The  spectra 
are  so  various  that  it  is  impossible  to  make  a  satisfactory 
classification  of  them.  Yet  by  considering  only  certain 
broad  characteristics  a  few  types  may  be  distinguished. 

Type  I.   This  type  embraces  the  white  or  bluish  stars,    sirians. 
which  are  far  more  numerous  than  others.   Sirius,  Vega, 
and  Altair  belong  to  it,    and  the  entire  group  is  often 
called  Sirian.     The  principal  lines  in  the  spectrum  are 


310 


A  Study  of  the  Sky. 


Solars. 


Variables. 


Deep  red  stars. 


Bright-line 
stars. 


due  to  hydrogen  ;  other  lines  are  faint  and  few.  Two 
thirds  of  these  stars  are  in  the  Milky  Way. 

Type  II.  Yellowish  stars  having  spectra  similar  to 
that  of  our  sun  are  placed  under  this  head  ;  such  are 
Pollux,  Capella,  and  Arcturus,  which  are  called  solar 
stars.  The  spectrum  is  rich  in  lines  belonging  to  vari- 
ous metals.  Solar  stars  are  distributed  equably  over 
the  heavens.  The  light  of  a  Sirian  star  is  more  in- 
tense than  that  of  a  solar,  but  the  latter  gives  on  the 
average  a  greater  quantity  of  light,  because  of  its  greater 
size. 

Type  III.  Orange  and  red  stars,  together  with  most 
of  those  which  fluctuate  in  brightness,  belong  to  this 
class,  which  includes  Betelgeuse  and  Antares.  Their 
spectrum  contains  many  dark  bands,  one  edge  of  which 
is  sharply  denned,  while  the  other  is  diffuse ;  the  sharp 
edge  is  on  the  side  next  to  the  violet  end  of  the  spec- 
trum. 

Type  IV.  The  stars  belonging  to  this  type  are  few  in 
number,  faint,  and  generally  of  a  deep  red  color.  The 
spectrum  is  banded  as  in  Type  III.,  but  the  sharper  edge 
of  each  band  is  on  the  side  next  to  the  red  end  of  the 
spectrum. 

More  than  fifty  stars  have  been  discovered,  whose 
spectra  are  different  from  any  of  the  preceding,  in  that 
they  contain  bright  lines,  thought  to  be  due  to  extensive 
gaseous  envelopes  enwrapping  them.  They  are  of 
especial  interest  because  they  seem  to  form  a  connecting 
link  between  nebulae  and  other  stars.  Bright  lines, 
thought  to  be  due  to  masses  of  vapor  hotter  than  the 
underlying  photosphere,  are  at  times  seen  in  the  spec- 
trum of  the  sun.  Most  of  the  stars  in  Orion  exhibit  a 
special  variety  of  spectrum,  which  is  not  often  met  out- 
side of  that  constellation. 


The  Fixed  Stars.  311 


So  many  different  varieties  of  spectra  are  known  that   The  universe 
Prof.  E.  C.  Pickering*  says  : 

In  general  it  may  be  stated  that  with  a  few  exceptions  all 
stars  may  be  arranged  in  a  sequence,  beginning  with  the 
planetary  nebulae,  passing  through  the  bright-line  stars  to  the 
Orion  stars,  thence  to  the  first  type  stars,  and  by  insensible 
changes  to  the  second  and  third  type  stars.  The  evidence  that 
the  same  plan  governs  all  parts  of  the  visible  universe  is  thus 
conclusive. 

The  opinion  that  different  spectra  belong  to  different  Ig  develo  ment 
stages  of  development  has  much  in  its  favor,  but  more  indicated? 
complete  investigations  must  be  made  before  any  far- 
reaching  theory  can    command   the    entire    consent  of 
spectroscopists. 

VARIABLE    STARS. 

Many  stars  are  inconstant  in  brightness,  and  bear  the 
designation  of  variables  ;  the  number  of  known  variables 
is  now  (1896)  nearly  four  hundred,  but  new  ones  are 
being  found  continually.  Certain  compact  clusters  con- 
tain a  large  number  of  variables.  They  are  not  included 
in  the  number  specified  above. 

The  most  marvelous  class  of  variables  is  the  tern-  Temporary 
porary  stars  which  appear  occasionally,  often  blazing  up 
with  a  wonderful  display  of  luminous  energy,  and  then 
fading  into  insignificance,  or  entire  invisibility.  Per- 
haps the  most  famous  of  these  is  Tycho's  star,  which  he 
perceived  while  out  walking  on  a  November  evening  in 
1572.  It  was  in  the  constellation  of  Cassiopeia,  and 
was  nearly  as  bright  as  Venus  at  her  best.  For  several 
days  it  was  visible  in  broad  daylight,  but  began  to  lose 
its  splendor  in  December  ;  fifteen  months  later  it  was 
too  faint  to  be  seen.  Tycho  measured  its  place  as  well 
as  it  could  be  done  without  the  aid  of  a  telescope, 

*  Director  of  the  Harvard  College  Observatory-. 


stars. 


3I2 


A  Study  of  the  Sky. 


Nova  Aurigse. 


A  strange 
spectrum. 


which  had  not  then  been  invented.  There  is  now  a 
faint  star  near  the  place  assigned  by  him,  but  it  is  not 
certain  that  the  two  objects  are  the  same. 

The  most  remarkable  recent  temporary  star  is  Nova 
Aurigae  (the  new  star  in  Auriga).  It  was  first  seen  by 
an  amateur  Scottish  astronomer  on  January  24,  1892, 

being  then  of 
the  fifth  magni- 
tude. It  had, 
ho\vever,  previ- 
ously impressed 
itself  on  a  pho- 
tographic plate 
exposed  at  Har- 
vard on  Decem- 
ber 10,  1891.  It 
was  not  on  a 
photograph  of 
the  same  region 
made  at  Heidel- 
berg on  Decem- 
ber 8.  It  must 
therefore  have 
burst  out  sud- 
denly between 
these  two  dates. 
Its  spectrum 
was  at  once  in- 
vestigated :  two  spectra  were  found  ;  one  was  a  bright- 
line  spectrum,  the  other  an  absorption  or  dark-line 
spectrum.  The  lines  in  the  two  spectra  were  not  in 
their  normal  positions,  but  were  shifted  in  such  a  way 
as  to  indicate  that  there  were  two  bodies  moving  in 
different  directions.  During  February  and  March  the 


FIG.  136. — A  RICH  PORTION  OF  THE  MILKY  WAY. 


The  Fixed  Stars.  313 


brightness  of  Nova  fluctuated  irregularly  ;  after  March 
6  its  magnitude  diminished  rapidly,  and  in  six  weeks  it 
was  barely  visible  in  the  Lick  telescope.  Four  months 
afterward  it  was  bright  enough  to  be  seen  in  a  three- 
inch  telescope,  and  looked  like  a  small  round  nebula. 
The  shifting  positions  of  the  spectral  lines  denoted  large 
and  variable  velocities,  and  are  very  difficult  to  explain. 

One  hypothesis  as  to  the  cause  of  the  outburst  is  that 
two  large  bodies  moving  swiftly  barely  missed  colliding,  Cause  of  the 
and  created  great  tidal  disturbances,  which  in  turn  led 
to  tremendous  eruptions  similar  to  solar  prominences, 
but  on  a  vastly  greater  scale.  Another  theory  is  that  a 
dark  body  plunged  into  some  cosmical  cloud,  like  the 
vast  nebulous  masses,  which  photography  reveals  here 
and  there.  When  it  passed  out  of  the  cloud  in  the 
spring  it  rapidly  cooled  off  ;  in  the  fall  it  encountered 
another  such  cloud,  which  brightened  it  up  again.  The 
observations  are,  however,  too  complicated  to  be  ex- 
plained fully  by  any  hypothesis  yet  advanced. 

Very  different  from  a  temporary  star  is  Algol,  the 
Demon  Star,  so  named  by  the  ancients  ;  it  is  in  the 
constellation  Perseus.  Usually  it  is  a  star  of  the  second 
magnitude,  but  at  regular  intervals  of  2d-  2ohrs>  48"""- 
56sec-  it  drops  to  the  fourth  magnitude  ;  it  remains  faint 
for  only  twenty  minutes,  and  brightens  again  until  it 
reaches  its  usual  luster.  Its  light  is  varying  during 
9hrs-  45min-  of  each  period.  The  periodical  darkening  is 
a  partial  eclipse  caused  by  a  dark  body  revolving  about 
a  bright  one  :  this  is  rendered  practically  certain  by 
spectroscopic  measurements,  which  show  that  Algol 
alternately  retreats  from  us  and  approaches  us,  just  as 
if  it  were  one  star  of  a  revolving  system.  The  dark 
companion  is  computed  to  be  of  nearly  the  same  size  as 
the  sun  ;  the  main  star  has  a  diameter  one  fifth  greater. 


A  Study  of  the  Sky. 


Mira. 


Irregular 
variations. 


Clusters. 


The  distance  between  their  surfaces  is  only  2,000,000 
miles.  Less  than  a  dozen  variables,  which  suffer  eclipse 
like  Algol,  are  known. 

Mira  (the  marvelous)  is  a  strange  variable  located  in 
Cetus  ;  its  changes  have  been  observed  for  three  hun- 
dred years.  It  occupies  eleven  months  in  running  the 
gamut  of  its  variations.  During  most  of  this  time  it  is 
invisible  to  the  naked  eye,  though  an  opera-glass  shows 
it  ;  but  once  in  eleven  months  it  rises  in  a  few  weeks  to 
a  maximum  brightness,  remains  thus  for  about  a  week, 
and  then  sinks  back  slowly  to  its  former  faintness,  the 
entire  change  occupying  three  months  and  a  fraction. 
Sometimes  its  greatest  brilliancy  does  not  equal  that  of 
the  faintest  of  the  seven  stars  in  the  Great  Dipper  ;  at 
other  times  it  rivals  the  brightest  of  them.  At  the  time 
of  a  maximum  its  spectrum  glows  with  a  profusion  of 
bright  lines.  The  strange  behavior  of  this  star 
and  others  of  its  class  may  be  explained  by  periodical 
eruptions  like  the  solar  prominences,  though  on  a  much 
larger  scale.  The  periodicity  of  such  eruptions  is  as 
mysterious  as  that  of  sun-spots. 

There  are  variables  which  are  unlike  Algol  or  Mira, 
some  of  them  being  seemingly  hopelessly  irregular  in 
their  variations.  The  cause  of  their  variability  can  only 
be  conjectured.  They  may  be  afflicted  with  enormous 
spots,  or  subject  to  collisions  with  meteoric  streams  ; 
great  protuberances  may  also  complicate  matters,  while 
rotation  upon  an  axis  may  tend  to  give  a  certain  regu- 
larity to  the  variations. 

Aggregations  in  which  the  stars  are  to  be  counted  by 
tens  or  hundreds  of  thousands  are  known  as  clusters. 
Several  of  the  stars  in  the  cluster  of  the  Pleiades  can  be 
seen  with  the  naked  eye,  and  many  more  are  brought 
out  by  an  opera-glass.  Praesepe  in  Cancer  and  the 


The  Fixed  Stars. 


315 


double  cluster  in  Perseus  look  like  bright  spots  on  the 
sky,  and  are  split  into  separate  stars  by  a  small  telescope. 
All  these  are  coarse  clusters. 

The  finest  compact   cluster  in    the  northern   hemis-  The  great 
phere   is   located    in   Hercules.     One  who    knows  just 


FIG.  137.— THE  GREAT  GLOBULAR  CLUSTER  IN  HERCULES. 

where  to  look  for  it  can  see  it  as  a  hazy  faint  star.  A 
large  telescope  is  needed  to  resolve  the  entire  cluster 
into  separate  stars.  It  is  globular  in  form,  and  near  its 
center  the  stars  appear  fairly  to  touch  one  another  ;  at 
the  edge  the  stars  are  more  scattered,  and  branch  out 
in  pretty  sprays.  Such  a  cluster  has  been  called  an 

/  '  ,-,  i  1     •  An  "island 

"island  universe,      as  though  it  were  a  system  apart  universe." 


A  Study  of  the  Sky. 


The  theory 
rejected. 


Is  the  universe 
spherical  ? 


from  other  stars,  sunk  in  well-nigh  infinite  depths  of 
space  ;  according  to  this  view  the  stars  which  appear  so 
crowded  are  really  separated  by  intervals  comparable 
with  the  distance  from  the  sun  to  Alpha  Centauri  or 
Sirius.  If  this  were  true  a  spectator  on  one  of  those 
distant  orbs  might  look  about  him,  and  see  a  heavens 
like  our  own,  spangled  with  novel  constellations,  and 
dotted  here  and  there  with  clusters,  one  of  which  con- 
tained our  own  sun  and  the  bright  stars  familiar  to  us. 

But  this  theory  is  no  longer  held.  In  certain  parts  of 
the  heavens  clusters,  nebulae,  and  individual  stars  of  va- 
rious degrees  of  brightness  are  so  associated  that  there 
is  little  probability  that  the  clusters  are  isolated  groups 
lying  at  inconceivable  distances  beyond  the  other  ob- 
jects. 

In  the  great  Hercules  cluster  each  star  must  be  sub- 
ject to  the  gravitating  influence  of  the  others  ;  but  no 
motion  has  been  detected  yet.  Photography  may  event- 
ually lead  to  the  detection  of  changes.  The  general 
opinion  is  that  the  cluster  in  Hercules,  and  others  of 
similar  appearance,  are  composed  of  much  smaller  stars 
than  the  sun. 

If  it  were  possible  to  survey  the  sidereal  universe 
from  without,  as  now  we  look  at  the  Hercules  cluster, 
would  it  too  appear  globular  ? 

The  first  fact  to  be  considered  is  that  the  vast  majority 
of  the  stars  lie  in  the  Milky  Way,  which  forms  a  girdle 
around  the  celestial  sphere.  Now  if  we  were  near  the 
center  of  a  spherical  cluster,  like  that  in  Hercules, 
throughout  which  the  stars  were  distributed  with  any 
approach  to  uniformity,  they  would  appear  to  be  about 
equally  numerous  in  whatever  direction  we  looked. 
There  would  be  no  point  within  the  sphere  from  which 
the  vast  majority  of  the  surrounding  stars  would  have 


The  Fixed  Stars.  317 


the  appearance  of  a  ring  like  the  Galaxy.  We  there- 
fore reject  the  hypothesis  of  sphericity  and  try  again. 

Suppose  that  an  aquarium  is  a  circle  ten  feet  in 
diameter,  in  which  the  water  is  a  foot  deep.  The  body  illustration  of 

an  aquarium. 

of  water  has  the  shape  of  a  thin  cheese.  Let  the 
aquarium  be  well  stocked  with  minnows,  and  let  a 
single  fish  somewhere  near  the  center  look  about  him. 
When  he  looks  horizontally,  no  matter  toward  what 
point  of  the  compass,  he  sees  a  goodly  number  of  his 
companions.  If  he  looks  straight  up  or  down  he  sees 
comparatively  few.  If  he  looks  obliquely  upward  or 
downward  he  sees  more  fish  than  when  he  looked 
straight  up,  and  fewer  than  when  he  looked  horizon- 
tally. If  he  had  an  agile  brain  and  pondered  over  the 
matter,  would  he  not  conclude  that  the  reason  why  he 
saw  the  most  fish  when  looking  horizontally,  was  that 
the  aquarium  extended  farthest  in  that  direction  ?  The 
more  he  studied  the  case  the  more  confident  would  he 
be  that  the  aquarium  was  cheese-shaped. 

Does  not  this  illustration  represent  what  an  astrono- 
mer sees  when  he  looks  about  ?  If  he  looks  toward  the 
Milky  Way,  which  appears  to  surround  him,  he  sees  a 
large  number  of  stars.  It  has  been  stated  that  the 
further  he  looks  from  the  Milky  Way  the  fewer  stars 
he  sees.  Is  it  not  reasonable  then  to  suppose  that  the 
sidereal  universe  occupies  a  space  shaped  somewhat  like 
a  thin  cheese  or  a  silver  dollar  ? 

But  more  persistent  inquiry  will  bring"  out  some  inter- 

r  .  -  The  solar 

esting  facts.  Those  stars  whose  distances  from  us  have  cluster, 
been  measured  are  mostly  bright,  and  are  scattered 
pretty  evenly  in  all  directions  from  us,  showing  no  tend- 
ency to  crowd  together  near  the  Milky  Way  ;  their 
spectra  are  chiefly  like  the  sun's  spectrum.  The  sun 
therefore  is  a  member  of  a  cluster  of  stars  similar  to 


A  Study  of  the  Sky. 


itself  in   composition   and  probably  globular   in  form. 

The  faint  stars  in  and  near  the  Milky  Way  are,  almost 

MUky°wa?nhe  without  exception,  at  distances  which  defy  our  powers  of 

measurement.     Of  faint  stars  of  any  particular  order  of 

brightness  those 
near  the  Milky  Way 
are  in  general 
further  from  us  than 
those  in  other  parts 
of  the  heavens. 
Shall  we  not  say 
then  that  most  of 
the  stars  in  the 
Milky  Way  consti- 
tute a  ring  sur- 
rounding us  ?  Stars 
whose  spectra  are 
like  that  of  Sirius 
are  very  abundant 
in  and  near  the  Gal- 
axy, and  scattered 
sparsely  in  other 
regions  ;  this  fact 
has  led  Professor 
Pickering  to  say 
that  the  Milky  Way 
may  well  be  regard- 
ed as  '  '  a  distinct 
cluster  of  stars,  to 

^^  frQm  ^  CQm_ 

position  or  its  age,  the  sun  does  not  seem  to  belong.  '  ' 
Saturn  on  a  The   mental   picture   of    the   stellar   universe    which 

springs  from  the  preceding  considerations  rudely  resem- 
bles the  planet  Saturn.     Within  is  a  ball  of  stars,    of 


FIG.  X38.-CLOUDY  REGION  IN  THE  MILKY  WAV. 


huge  scale. 


The  Fixed  Stars.  319 


which  the  sun  is  one.  Surrounding  the  ball  is  an  irregu- 
lar ring  composed  of  faint  stars  in  and  adjacent  to  the 
Milky  Way.  Such  a  theory  as  this  cannot  be  consid- 
ered final,  but  it  commends  itself  as  the  best  that  can  be 
devised  in  the  light  of  present  knowledge. 

Our  next  inquiry  is  about  the  motion  of  this  stupen- 

.««,,.«  r  Proper  motions 

dous  system  ;  the  only  available  light  comes  from  a  of  stars, 
study  of  the  movements  of  a  great  many  stars  scattered 
in  all  parts  of  the  heavens.  Many  stars  are  moving 
slowly  across  the  face  of  the  sky,  despite  their  designa- 
tion of  fixed  stars.  Star  No.  1830  in  Groombridge's 
catalogue  moves  a  degree  in  five  hundred  years.  Arc- 
turus,  which  also  has  a  large  proper  motion,  has  shifted 
its  position  by  an  equal  amount  during  the  Christian  era. 
Such  rapid  motions  are  quite  exceptional.  If  a  star  is 
moving  toward  us  or  from  us,  its  velocity  of  approach  or 
recession  is  obtained  by  spectroscopic  observations  ;  no 
velocity  yet  measured  exceeds  fifty  miles  a  second.  A 
star  which  is  moving  directly  toward  us,  or  away  from 
us,  has  no  "  proper  motion,"  because  it  does  not  alter 
its  position  on  the  face  of  the  sky. 

Many  groups  of  stars  have  a  common  proper  motion. 
Only  a  few  out  of  four  hundred  stars  in  the  Pleiades,  whose  have  a  common 

*  .  motion. 

proper  motions  have  been  measured,  refuse  to  drift  along 
in  the  same  direction  as  the  others.  It  may  almost  be  laid 
down  as  a  principle  that  most  of  the  stars  in  any  group 
drift  together,  as  though  they  were  really  connected. 

The  stars  are  going  in  all  directions,   so  that  it  seems   A  revailin 
impossible   to   deduce  any  general  results  about   their  drift, 
movements.      But  patient  study  of    large  numbers    of 
proper  motions  has  clearly  brought  out  a  prevailing  drift. 
Stars  in  Hercules  and  Lyra  are  spreading  apart  very 
slowly  ;  those  on  the  opposite  side  of  the  celestial  sphere 
are  coming  together. 


320 


A  Study  of  the  Sky. 


Is  there  a 
central  sun  ? 


Various 
systems. 


Is  there  evi- 
dence of  design? 


A  passenger  on  a  ferry-boat  plying  between  two  cities 
at  night  sees  lights  along  the  wharves  of  each  city.  The 
lights  in  one  set  are  spreading  apart ;  in  the  other  they 
are  coming  closer  together.  He  knows  at  once  that  he 
is  going  toward  the  spreading  lights.  In  like  manner 
the  astronomer  concludes  that  the  sun,  carrying  along 
its  family  of  planets,  is  moving  toward  that  region  of 
the  heavens  which  Hercules  and  Lyra  grace.  Whether 
the  sun  is  moving  in  a  straight  line,  or  in  the  majestic 
sweep  of  some  grand  orbit,  cannot  yet  be  decided. 

There  is  a  persistent  idea  that  there  exists  a  central 
sun,  about  which  all  the  starry  hosts  move  obediently 
in  vast  cycles  of  time.  But  the  motions  of  the  stars  are 
so  complex  that  no  one  can  hope  to  locate  a  point  about 
which  all  bodies  in  the  universe  revolve. 

There  are  hosts  of  subsidiary  systems,  which  are 
orderly  in  their  ongoings.  The  solar  system  is  ruled 
despotically  by  the  sun.  Binary  systems  move  in 
proper  fashion,  bound  by  a  common  tie.  The  stars 
composing  a  group  like  the  Pleiades  seem  to  be  im- 
pelled toward  a  common  goal.  Thus  the  entire  sidereal 
universe  is  composed  of  groups  which  are  practically 
independent  of  one  another.  There  is,  in  the  present 
state  of  astronomical  knowledge,  no  inkling  of  a  general 
plan  in  accordance  with  which  all  the  stars  move. 

But  the  design  of  the  Creator  may  not  involve  any 
particular  form  of  orderly  movement  which  the  mind  of 
man  has  yet  conceived.  The  fact  that  the  molecules 
which  compose  a  marble  statue  do  not  revolve  about  a 
common  center,  or  move  in  curves  whose  sinuosities 
can  be  embraced  in  a  formula,  does  not  detract  from  its 
beauty,  or  argue  the  absence  of  design.  The  entrancing 
beauty  shines  forth,  and  speaks  eloquently  of  the  cun- 
ning hand  of  the  sculptor. 


CHAPTER    XVIII. 

THE    NEBULA. 

"  Regions  of  lucid  matter  taking  forms, 
Brushes  of  fire,  hazy  gleams." 

—  Tennyson. 

NEBULAE  are  cloud-like  masses,  of  a  great  variety  of 

Different 

form.  Planetary  nebulae  are  small  and  round  ;  they  are  classes  of 
usually  somewhat  brighter  in  the  center  than  at  the 
edge.  If  there  is  a  very  marked  central  condensation, 
the  object  may  be  called  a  nebulous  star.  Annular 
nebulae  are  ring-shaped,  brighter  at  the  edge  than  near 
the  center.  Spiral  nebulae  exhibit  coils,  like  those  of  a 
watch-spring,  or  a  corkscrew.  The  largest  nebulae  are 
irregular  in  form  and  enormous  in  extent,  being  the 
largest  visible  objects  in  the  universe  ;  they  dwarf 
everything  else  into  insignificance.  Photographs  of 
Orion  show  that  a  large  part  of  the  constellation  is 
involved  in  a  great  nebula.  Many  clusters  contain 
nebulous  matter  within  their  boundaries  ;  large  nebulae 
often  appear  to  shelter  stars  within  their  ample  folds. 

About  8,500  are  now  known  ;  new  ones  are  being 
continually  discovered.  Photography  offers  a  distinct 
advantage  for  the  work  of  discovery,  since  the  sensitive 
film  captures  objects  too  faint  to  impress  the  eye.  They 
are  not  scattered  uniformly  over  the  sky  ;  near  the 
Milky  Way  few  are  to  be  found.  Where  stars  are  few 
nebulae  abound,  being  most  numerous  near  the  galactic 
poles,  as  previously  stated. 

No  one  has  succeeded  in  measuring  the  distance  of  a 
321 


322 


A  Study  of  the  Sky. 


Distances. 


nebula,  though  repeated  attempts  have  been  made  upon 
planetary  nebulae.  No  nebula  invites  such  an  attack, 
unless  it  has  some  nuclear  point  which  can  be  bisected 


Association 
with  stars. 


FIG.  139.— A  SPIRAL  NEBULA. 

with  the  spider-web  of  a  micrometer.  Yet  they  are 
in  many  cases  so  associated  with  stars  that  one  cannot 
doubt  that  they  are  at  the  same  distances. 


The  Nebula.  323 


In  the  Pleiades  nebulous  wisps  connect  certain  stars  ; 
some  of  the  brighter  stars  of  the  cluster  are  involved  in 
nebulosity.  The  sextuple  star  Theta  Orionis  lies  in  a 
dark  place  in  the  great  nebula  in  Orion.  The  appear- 
ance suggests  that  some  of  the  adjacent  nebulous  matter 
has  been  used  up  in  forming  the  stars.  Four  groups  of  similar  spectra 
lines  in  the  spectrum  of  the  stars  coincide  with  corre- 
sponding groups  in  the  spectrum  of  the  nebula,  and 
render  it  very  probable  that  the  stars  actually  lie  in  the 
nebula,  instead  of  being  merely  in  line  with  it.  The 
nebula  therefore  is  at  the  same  distance  as  the  stars. 

As  spectroscopic  observations  have  shown,  their  ve-   Motjons 
locities  are  of  the  same  magnitude  as  those  of  stars. 

Drawings  of  a  given  nebula  made  at  the  same  time  by 
observers  using  different  instruments  vary  so  much  in 
detail  that  a  comparison  of  one  set  of  drawings  with  an- 
other gives  no  secure  evidence  of  change  in  the  form  of 
the  nebula.  The  case  of  the  trifid  nebula  in  Sagittarius 
deserves  mention  in  this  connection.  It  contains  a 
curious  dark  rift,  in  which  Herschel  and  other  observers 
saw  a  triple  star,  in  the  early  part  of  the  nineteenth  cen- 
tury. This  star,  which  has  not  moved  appreciably  with 
reference  to  other  stars  in  the  vicinity,  now  lies  in  the 
edge  of  the  nebulous  matter  adjacent  to  the  rift.  The 
nebula  must  either  have  changed  its  form  or  drifted. 
While  the  outlines  of  the  central  portion  of  the  great 
nebula  in  Orion  remain  unchanged,  there  are  anoma- 
lous variations  in  the  brightness  of  different  portions  of  it. 

Most  of  the  nebulae  are  too  faint  to  give  perceptible 
spectra.  About  half  of  the  spectra  thus  far  examined  Spectra. 
are  composed  of  a  few  bright  lines,  which  come  from 
glowing  gases.  The  presence  of  incandescent  hydro- 
gen is  amply  demonstrated  ;  helium  is  fairly  recognized, 
and  also  sodium.  The  remaining  spectra  are  chiefly 


324 


A  Study  of  the  Sky. 


The  Androm- 
eda nebula. 


continuous  bands  of  color  such 
as  would  be  given  by  heated 
liquid  or  solid  bodies,  or  gases 
subjected  to  great  pressure.  A 
few  nebulae  give  both  spectra. 
Nebulae  may  contain  solid  or 
liquid  bodies  which  are  not  suffi- 
ciently luminous  to  manifest 
themselves. 

The  great  nebula  in  Androm- 
eda is  easily  seen  with  the 
naked  eye.  A  small  telescope 
shows  that  it  has  a  bright  ball 
near  the  center,  and  is  spindle- 
shaped.  The  magnificent  pho- 
tographs taken  of  late  years 

FIG.  140.— THE  NEBULA  OF 

ORION  PHOTOGRAPHED.       reveal  a  very  interesting  struc- 

Exposure,  fifteen  minutes. 

ture.  The  whole  rudely 
resembles  Saturn,  the  cen- 
tral ball  being  surrounded 
by  a  ring  ;  in  the  ring  are 
dark  curved  lanes,  as 
though  the  structure  was 
spiral.  Two  smaller  balls 
outside  of  the  ring  sug- 
gest planets  yet  uncon- 
densed.  There  appeared 
in  1885  close  to  the  nu- 
cleus of  the  nebula  a  new 
star  which  could  be  seen 
with  an  opera-glass  ;  in  a 
few  months  it  had  van- 

•  11        _  111  PIG.  I4-1' — THE  NEBULA  OF  ORION  PHO- 

ISneCl.       It  Was  probably  a         xoGRAPHiiD.     Exposure,  two  hours. 


The  Nebula. 


325 


fortuitous  condensation  or  local  brightening  of  the  nebu- 
lous matter,    its  spectrum  being  like  that  of  the  nebula. 
The  great  nebula  in  Orion  is   the  most  wonderful  in 
the  heavens.      Its  most  brilliant  portion  is  in  the  sword-   The  nebula 

*  in  Orion. 

handle  of  the  giant.     One  easily  sees  there  three  stars 
in  a  row  ;  the  middle  star  is  surrounded  by  a  feeble  glow 


FIG.  142.— THE  NEBULA  OF  ORION  PHOTOGRAPHED.     Exposure,  nine  hours. 

coming  from  the  nebula.  Galileo  has  left  no  record  of  it, 
much  as  he  scoured  the  heavens.  Cysatus,  who  was 
following  a  comet  in  1618,  first  came  across  it,  and  com- 
pared the  comet  with  it.  As  telescopes  improved,  the 
star  which  it  envelops  was  split  into  four,  called  the 
Trapezium  ;  later  two  more,  were  added  to  the  four. 
Dark  spots  were  seen  in  the  cloud,  and  enormous  wing- 
like  extensions  of  faint  nebulosity,  which  gave  the  neb- 


The  Trape- 
zium. 


326  A  Study  of  the  Sky. 

ula  the  appearance  of  a  ghostly  bat  of  prodigious  size. 
The  spectroscope  then  revealed  the  bright-line  spectrum 
of  glowing  gas,  though  portions  of  the  nebula  have 
square  corners  and  bright  ribs  and  dark  vacuities. 
Finally  photography  scored  a  signal  triumph  by  extend- 
ing the  nebula  in  wraith-like  arms  which  embrace  a  large 
part  of  Orion.  Perhaps  the  exceptional  richness  of  the 
constellation  is  due  to  the  vastness  of  the  nebular  quarry 
from  which  the  stars  were  hewn. 

"  Where  striving  o'er  the  dim,  ethereal  plain, 
Orion  brandishes  his  flaming  sword, 
And  shakes  ajar  the  awful  vestibule 
Of  heaven's  stupendous  treasury  of  suns, 
Set  for  a  jewel  in  the  mighty  hilt." 

The  Magellanic  clouds,  or  nubecuke,  are  invisible  in 

The  Magellanic 

clouds.  the  United  States,  because  they  are  too  near  the  south 

celestial  pole.  They  resemble  detached  sections  of  the 
Milky  Way,  the  larger  one  being  of  the  size  of  the  bowl 
of  the  Great  Dipper,  while  the  smaller  is  one  fourth  as 
large.  These  marvelous  aggregations  may  well  be 
likened  to  celestial  show-cases,  in  which  are  displayed 
specimens  of  sidereal  wonders.  While  nebulae  and 
clusters  fight  shy  of  one  another  in  other  parts  of  the 
heavens,  they  are  here  mingled  indiscriminately.  Glob- 
ular clusters  are  found  in  all  stages  of  condensation,  and 
irregular  clusters  of  various  degrees  of  coarseness.  Ir- 
regular nebulae  of  curious  forms,  and  neat  little  elliptical 
ones,  are  thickly  scattered  over  a  background  rich  in 
stars.  In  places  the  stars  are  minute  and  packed  as 
though  they  were  the  closely  woven  texture  of  a 
celestial  fabric. 

A  peculiar  interest  inheres  in  the  study  of  nebulae, 
since  they  are  thought  to  be  the  chaotic  world-stuff  from 
which  stars,  clusters,  suns,  planets,  and  satellites  have 


The  Nebulce.  327 


been  evolved.  Milton  adumbrates  this  idea  in  the 
second  book  of  ''Paradise  Lost,"  where  he  describes 
Satan  pausing  a  moment  at  the  open  mouth  of  hell,  ere 
he  set  out  across  the  abyss  which  lay  before  him,  seek- 
ing for  the  abode  of  man. 

"  Into  this  wild  abyss, 

The  Womb  of  Nature,  and  perhaps  her  grave, 
Of  neither  sea,  nor  shore,  nor  air,  nor  fire, 
But  all  these  in  their  pregnant  causes  mixed. 
Confusedly,  and  which  thus  must  ever  fight, 
Unless  the  Almighty  Maker  them  ordain, 
His  dark  materials  to  create  new  worlds  : 
Into  this  wild  abyss  the  wary  fiend 
Stood  on  the  brink  of  hell,  and  looked  awhile, 
Pondering  his  voyage  :  for  no  narrow  frith 
He  had  to  cross." 

Men  may  properly  be  abashed  before  the  problem  of 

J    r  J  .  The  nebular 

the  development  of  the  universe,  but  they  have  not  hypothesis, 
hesitated  to  attack  it,  working  out  a  theory  concern- 
ing the  origin  of  the  solar  system,  and  following  the 
same  line  of  thought  with  reference  to  the  countless 
bodies  which  make  up  the  sidereal  heavens.  The 
famous  hypothesis,  which  has  been  slowly  elaborated 
during  a  century  and  a  half,  is  familiarly  known  as  the 
"  nebular  hypothesis."  Suggested  by  Kant  and  Swed- 
enborg  it  was  treated  from  a  mathematical  standpoint  by 
Laplace  at  the  close  of  the  eighteenth  century.  Since 
that  time  it  has  undergone  modification  in  details,  but 
the  outline  of  the  original  fabric  of  thought  remains. 

According  to  this  theory  the  materials  which  are  now 
to  be  found  in  the  sun  and  planets  were  originally  Ofthe1§arlng 
diffused  through  a  nebula  of  vast  extent.  The  nebula 
may  have  been  a  mass  of  heated  gas,  but  was  probably 
a  cloud  of  cold  dust.  The  mutual  attractions  of  its 
particles  caused  it  to  assume  a  globular  form,  to  acquire 


328  A  Study  of  the  Sky. 

a  rotatory  motion,  and  to  become  hotter.  The  smaller 
it  became,  the  more  rapidly  it  whirled  ;  it  was  flattened 
at  the  poles  and  bulged  at  the  equator.  The  ' '  cen- 
trifugal force ' '  finally  became  so  great  that  the  central 
attraction  could  no  longer  restrain  matter  in  the  equa- 
Rings  or  more  torial  regions,  and  a  ring  escaped  at  the  equator.  Or 

compact  masses  . 

are  left  behind,  if  there  were  some  place  on  the  equator  where  the 
matter  was  denser  than  in  adjoining  regions,  a  lump 
was  formed  at  this  dense  spot,  and  the  lump  was  left  be- 
hind, instead  of  a  ring. 

The  original  body  rotated  still  more  swiftly  ;  another 

Formation  of  rmg  or  another  ball  was  liberated.  If  some  portion  of 
an  abandoned  ring  was  markedly  more  dense  than  the 
rest  of  it,  it  gradually  attracted  to  itself  the  adjacent 
matter,  and  finally  formed  another  rotating  body  (a 
planet),  which  in  turn  threw  off  rings  or  balls  of  matter 
to  form  satellites.  If  a  ring  were  pretty  homogeneous 
it  might  condense  into  a  multitude  of  bodies  like  the 
asteroids,  or  the  rings  of  Saturn,  which  are  by  some 
considered  an  ear-mark  of  the  creative  process. 

A  liberated  ball  would  form  a  planet  more  quickly 

Further  history  t^ian  a  rm%  wou^-     The  planets  and  satellites  gradually 

of  the  planets,  liquefied  and  solidified,  falling  in  temperature  at  the 
same  time.  Minute  bodies  like  the  satellites  of  Mars 
lost  their  heat  quickly,  and  are  probably  now  solid 
throughout.  On  larger  bodies  a  crust  was  formed,  and 
the  central  fires  have  not  yet  died  out  ;  such  is  the  case 
of  the  earth.  Still  larger  bodies,  like  Jupiter  and 
Saturn,  have  probably  not  cooled  off  sufficiently  to  per- 
mit the  formation  of  a  solid  crust.  The  sun,  which 
holds  in  fiery  embrace  most  of  the  matter  in  the  original 
nebula,  will  begin  to  cool  off  whenever  his  huge  mass 
begins  to  liquefy. 

Such  is  the  nebular  hypothesis,  briefly  stated.     Some 


The  Nebulce, 


329 


years  ago  it  was  supposed  that  the  retrograde  motions 

of  the  satellites  of  Uranus  and  Neptune,  and  the  rapid  objections. 

motion   of  the  inner  moon   of  Mars,    which  completes 

a  revolution  in  less  than  one  third  of  a  Martian  day,  were 

objections   to   the   theory.     But  these   anomalies    have 

now  received  satisfactory  explanations. 

Let   us   now   travel   in   imagination   throughout   the 


FIG.  143.— A  DRAWING  OF  THE  CENTRAL  PART  OF  THE  GREAT  NEBULA 
IN  ORION. 

universe,  investigating  the  nebulae,  the  stars,  the  earth,    Abroadinves- 
the  moon,    the  planetary  system,   and  finally  the  sun,   ^*tt*OBt 
that  they  may  give  their  mute  testimony  to  the  truth  or 
falsity  of  the  nebular  hypothesis. 

Scattered  over  the  sky  we  find  vast  inchoate  masses   The  raw 
of  faintly  gleaming  matter,  some  of  the  most  stupendous  matenal- 
of  which  are  revealed  by  photography  alone,  being  too 
faint  for  the  most  powerful  visual  apparatus.     Surely 
here  is  the  raw  material  which  the  theory  demands. 


330 


A  Study  of  the  Sky. 


The  next  step. 


The  nebula 
in  Orion. 


Planetary 
nebulae. 


The  Pleiades. 


Other  associ- 
ations of  nebulae 
and  stars. 


The  next  step  in  the  process  is  illustrated  by  the  great 
nebula  in  Andromeda,  in  the  center  of  which  is  a  bright 
globe.  The  surrounding  matter  is  arranged  in  rings  or 
whorls,  as  if  there  were  a  motion  of  rotation,  disengag- 
ing rings  of  tenuous  matter.  Has  any  of  the  disengaged 
material  assumed  a  spherical  form  ?  Look  again  at  this 
wonderful  nebula  and  see  the  two  outlying  globes. 

Study  the  latest  photograph  of  the  nebula  in  Orion, 
and  let  the  gigantic  spiral  tell  its  own  story.  See  the 
stars  in  the  Trapezium,  and  the  dark  space  in  which  they 
lie,  as  if  some  of  the  nebulous  matter  had  been  used  up 
in  forming  them.  Examine  their  spectra  and  behold 
the  bright  lines,  which  tally  with  lines  in  the  spectrum 
of  the  nebula.  Does  not  a  heated  gas  produce  a  spec- 
trum of  bright  lines  ? 

Pass  in  review  hundreds  of  planetary  nebulae.  Are 
they  not  circular  ?  Have  not  some  of  them  faint  con- 
densations in  their  centers  ?  Have  not  some  brighter 
condensations  ?  Do  not  a  considerable  number  exhibit 
a  spiral  structure  ?  Can  we  not  arrange  known  nebulae 
in  orderly  sequence  from  those  composed  of  the  dim- 
mest world-stuff  up  to  those  which  have  justly  received 
the  appellation  of  nebulous  stars  ?  Is  the  testimony  of 
the  nebulae  inconclusive  ?  We  turn  to  the  stars. 

Let  us  study  various  photographs  of  the  Pleiades. 
Why  does  a  nebulous  bridge  run  from  this  faint  star  to 
its  neighbor  if  there  be  no  relation  between  nebulae  and 
stars?  Why  does  this  other  nebulous  ray  connect  a  row 
of  small  stars  ?  Why  are  so  many  of  the  brighter  stars 
apparently  involved  in  nebulosity  ?  Why  do  rays  run 
out  from  this  large  nebula  to  these  faint  stars  ? 

Why  are  there  so  many  stars  all  over  the  heavens 
which  appear  to  be  enveloped  with  nebulous  matter  ? 
How  are  certain  very  complicated  stellar  spectra  to  be  ex- 


The  Nebula.  331 


plained  ?     Are  not  the  stars  giving  them  surrounded  by 
enormous  gaseous  envelopes  ? 

Has  not  our  attention  been  already  called  to  the    fact  Is  there  a 
that  almost  all  stars  can  be  arranged  in  a  sequence  from  sequence? 
planetary   nebulae  onward  to  the  most  highly  finished 
orbs,  according  to  the  characteristics  of  their  spectra  ? 
While  this  is  true,  let  us  be  candid  and  admit  that  such 
a  sequence  must  be  considered  only  as  a  possible  hint  of 
progressive  development. 

Is  the  testimony  of  the  nebulae  and  stars  insufficient  ? 
We  turn  to  the  earth. 

Is  the  earth  a  cold,  dark,  solid  body,  far  removed  in  Tfae  ^^ 
nature  from  the  heated  objects  which  we  have  consid- 
ered thus  far?  Take  a  thermometer  down  deep  holes  in 
the  earth's  crust,  and  see  the  column  of  mercury  slowly 
rise.  Listen  to  the  rumbling  of  yonder  volcano ;  see  the 
steamy  cloud  rising  from  it,  and  the  scorching  outpour- 
ings which  have  rolled  down  its  sides  ;  ask  the  geologist 
whether  the  granite  of  our  mountains  has  ever  passed 
through  primeval  fires.  Give  heed  to  his  statement  that 
statuary  marble  is  limestone  transformed  by  heat.  Is 
there  not  a  preponderance  of  evidence  in  favor  of  the 
view  that  mountain  chains  are  wrinkles  of  the  earth's 
crust  formed  while  it  was  contracting  ?  Is  there  no  hint 
in  the  fact  that  if  the  earth  were  heated  to  incandescence 
its  spectrum  would  resemble  the  sun's  ? 

Is  the  testimony  of  the  nebulas,   the  stars,   and  the 
earth  inconclusive  ?     We  turn  to  the  moon. 

He   who   examines  the  moon  with  a  telescope  and  The  moon, 
studies  its  formations  will  hardly  deny  that  indications 
of  an  igneous  origin  are  written  in  large  characters  over 
its  scarred  visage.   On  this  point  let  us  listen  to  Nasmyth 
and  Carpenter,  two  English  students  of  the  moon  : 

We  trust  then  that  we,  on  our  part,  have  shown  that  the 


332 


A  Study  of  the  Sky. 


A  medal  of 
creation. 


The  sun. 


study  of  the  moon  may  be  a  benefit  not  merely  to  the  astrono- 
mer, but  to  the  geologist,  for  we  behold  in  it  a  mighty  medal 
of  creation,  doubtless  formed  of  the  same  material  and  struck 
with  the  same  die  that  molded  our  earth,  but  while  the  dust  of 
countless  ages  and  the  action  of  powerful  disintegrating  and 
denuding  elements  have  eroded  and  obliterated  the  earthly 
impressions,  the  superscriptions  on  the  lunar  surface  have  re- 
mained with  their  pristine  clearness  unsullied,  every  vestige 
sharp  and  bright  as  when  it  left  the  Almighty  Maker's  hand. 

Is  the  testimony  of  the  nebulae,  the  stars,  the  earth, 
and  the  moon  insufficient  ?  We  turn  to  the  planetary 
system,  and  group  some  observed  harmonies  under  four 
heads. 

I.  Jupiter,   Saturn,   Uranus,    and  Neptune  are  large 
bodies   of    small   density.      According   to  the   nebular 
theory  were  they  not  formed  from  large  rings  of  small 
density  ?     Mars,  the  earth,  Venus,  and  Mercury,  on  the 
other  hand,  are  small  bodies  of  great  density. 

II.  All  the  planets  revolve  eastward  about  the  sun, 
their  orbits  being  nearly  circular,  and  lying  nearly  in  the 
same  plane. 

III.  All  the  known  rotations  of  the  planets  are  east- 
ward, the  planes  of  their  equators  being  nearly  coinci- 
dent with  those  of  their  orbits. 

IV.  The  satellites  of  the  planets  revolve  in  planes 
which  do  not  deviate  much  from  the  equators  of  their 
primaries  ;  they  also  revolve  in  the  direction  in  which 
their  primaries  rotate.     The  positions  of  the  planes  of 
the  equators  of  Uranus  and  Neptune  are,  however,  un- 
known. 

Is  the  testimony  of  the  nebulae,  the  stars,  the  earth, 
the  moon,  and  the  planetary  systems  insufficient  ?  We 
turn  to  the  sun. 

It  has  been  stated  that  the  sun's  outpour  of  radiant 
energy  is  accounted  for  by  the  supposition  that  it  is 


The  Nebula.  333 


slowly  contracting  in  bulk.  If  it  is  contracting,  was  it 
not  larger  one  thousand  years  ago  than  to-day  ?  Was  it 
not  still  larger  one  hundred  thousand  years  ago  ?  Can 
we  not  go  back  in  thought  through  the  long  ages  of 
which  geologists  tell  us,  and  see  the  sun  larger  yet  and 
more  diffuse  ?  If  we  may  be  bold  to  peer  into  appalling 
abysses  of  past  time,  do  we  not  at  last  see  in  dim  out- 
line the  mists  of  a  gigantic  nebula,  from  which  the  solar 
system  has  been  formed  by  such  a  process  as  we  have 
sketched  ? 

Is  not  the  chain  of  evidence  so  complete  as  to  compel 

.,       Tr  4.U-  t        A-  u      •  What  shall 

our  assent  ?      It  this  were  a  matter  ot  ordinary  business,    we  say  ? 
if  shares  of  stock  in  the  nebular  hypothesis  were  for  sale, 
would  you  not  consider  them  a  good  investment  ? 

If  you  were  to  consult  an  astronomer,  before  making 
this  intellectual  investment,  what  would  he  say  ?  He  mer's  opSSon. 
would  reply  that  if  you  wished  to  invest  in  an  hypothe- 
sis, he  could  heartily  recommend  the  nebular  hypothesis; 
he  himself  had  taken  stock  in  it.  But  he  would  beg 
you  to  remember  that  there  is  a  vast  difference  between 
an  hypothesis  and  an  ascertained  fact,  and  that  this 
particular  hypothesis  could  never  attain  the  certainty  of 
a  demonstration.  He  would  remind  you  that  a  man 
who  has  a  limitless  duration  of  time  to  draw  upon,  and 
an  infinite  extent  of  space  to  put  the  creations  of  his 
imagination  in,  ought  to  be  able  to  invent  a  far-reaching 
theory  which  would  seemingly  agree  with  almost  any 

J     1  (  t  TU         t  •     j  Possible  over- 

orderly  series  of  facts.      Though  it  does  not  now  seem  at  throw  of  the 

,all  probable,  yet  it  is  possible  that  in  the  centuries  to 
come  new  facts  may  be  discovered  and  new  laws  formu- 
lated, to  which  the  nebular  hypothesis  will  be  compelled 
to  yield,  as  the  Ptolemaic  theory  yielded  after  fourteen 
centuries  to  the  Copernican,  and  as  Newton's  corpuscu- 
lar theory  of  light  gave  way  to  the  wave  theory. 


334 


A  Study  of  the  Sky. 


The  subtlety 
of  nature. 


A  glance  ahead. 


The  stars 
die  out. 


Some  day  the  wreck  of  the  nebular  hypothesis  may 
furnish  a  fresh  illustration  of  the  doctrine  of  Bacon  that 
the  subtlety  of  nature  transcends  in  many  ways  the 
subtlety  of  the  intellect  and  senses  of  man,  and  may  call 
men's  attention  anew  to  the  real  depth  of  their  igno- 
rance concerning  the  fundamental  causes  of  natural 

phenom  en  a. 
Ac  r  oss  the 
chasm  of  centu- 
ries still  rings 
the  old  poetic 
outburst,  ' '  Lo, 
these  are  parts 
of  His  ways  ; 
but  how  little  a 
portion  is  heard 
of  Him?  but  the 
thunder  of  His 
power  who  can 
understand  ? ' ' 

We  have  been 
threading  the 
mazes  of  the 
past :  what  shall 
we  say  of  the 

FIG.  144.— THE  RING  NEBULA  IN  LYRA.  future  ?       In  the 

chapter  on  the  sun  we  have  already  considered  the 
future  of  the  solar  system,  and  we  now  turn  to  the 
sidereal  universe. 

The  stars  seem  to  be  radiating  away  their  stores  of 
energy,  just  as  the  sun  is.  The  best  light  that  we  have 
reveals  Arcturus  the  magnificent  or  Sirius  the  glowing 
as  a  dull  cold  corse,  when  ages  have  rolled  away.  If 
these  stellar  princes  are  at  last  to  sink  into  eternal  night, 


The  Nebula.  335 


shall  we  not  prophesy  the  same  fate  for  the  lesser  orbs  ? 

To  be  sure,  their  places  may  be  rilled  by  new  stars   Newonesa 
condensed  from  nebulae  now  seen  and  from  others  which  Pear  and  die 

in  turn. 

are  not  yet  bright  enough  to  show  themselves.  But 
the  death  knell  of  these  new  worlds  must  be  sounded  at 
last,  unless  there  be  some  intervention  of  which  we  have 
no  hint. 

If  such   be  the   fate    of   the   sidereal   universe,    why 

J     Why  repine  i 

should  we  repine  ?  If  our  reasoning  be  correct  the 
human  race  will  perish  long  before  the  sidereal  universe 
loses  the  splendid  energies  whose  manifestations  bring 
us  so  much  delight.  We  have  no  evidence  that  there 
are  inhabitants  of  other  worlds,  who  would  be  over- 
whelmed in  the  universal  rout.  The  peopling  of  planets 
surrounding  other  suns  with  intelligences  is  but  a  vagary 
of  the  fancy. 

If  the  Creator  spoke  the  universe  into  existence,  may  The  Creator 
he  not  speak  it  out  of  existence,  when  once  it  has  ful-  1S  suPreme- 
filled  his  purposes  ?  But  let  us  call  a  halt,  ere  we  wander 
further  in  paths  of  groundless  and  fruitless  speculation. 
We  may  rest  in  the  assurance  that  He  who  has  con- 
trolled the  worlds  for  ages  past  still  holds  them  in  the 
hollow  of  His  hand,  and  orders  their  destinies  aright. 
Radiant  suns  are  not  needed  to  shed  light  arid  heat 
upon  the  City  Beautiful,  whose  walls  are  jasper  and 
whose  gates  are  pearl.  "  For  the  glory  of  God  doth 
lighten  it  and  the  Lamb  is  the  light  thereof. ' ' 


INDEX. 


Achromatic  telescope,  131. 

Adam,  17,  20. 

Adams,  J.C.,  269. 

^Esculapius,  107. 

Age  of  the  sun,  204. 

Albireo,  98. 

Alcor,  45,  60. 

Alcyone,  73. 

Aldebaran, 53, 72. 

Algol,  81,  305,  313. 

"Almagest,"  24,  26. 

Alpha  Centauri,  305. 

Alphabet,  Greek,  55. 

Alphonso,  26. 

Altair,  53,  105. 

Andromeda,  37,  39,  48,  69,  324,  330. 

Andromedes,  290,  292. 

Angular  measurement,  41. 

Antares,  53,  101,  102. 

Apennines,  214,  216. 

Aphelion,  237. 

Aquarius,  66. 

Aquila,  53, 105. 

Arabian  astronomy,  25. 

Arcturus,  36,  53,  87. 

Aries,  70. 

Arion,  104. 

Aristotle,  23. 

Aryans,  20. 

Asteroids,  39,  246. 

Astronomers,  in. 

Auriga,  76. 

Australian  savages,  52. 

Babylonian  astronomy,  22. 

Bacon,  128. 

Barnard,  E.  E.,  120,  250,  259,  264. 

Bayer,  53. 

Bede,  50. 

Betelgeuse,  53,  74,  75. 

Biela's  comet,  281,  284,  293. 

Binary  stars,  306. 

Bloomington,  299. 


Bode's  law,  247. 

Bootes,  53,  87. 

Brashear,  J.  A.,  137. 

Bread,  180. 

Brenham  township,  299. 

Brightness  of  stars,  57. 

Brooks,  W.  R.,  286,  287. 

Burnham,  S.  W.,  126. 

Campbell,  W.  W.,  245. 

Canals  of  Mars,  240. 

Cancer,  83,  94. 

Canis  Major,  83. 

Canis  Minor,  85. 

Capella,  36,  37,  76,  77,  84,  305. 

Capricornus,  109. 

Capture  of  comets,  273. 

Cassiopeia,  48,  62. 

Castor,  79. 

Catalogue  of  stars,  54,  55. 

Celestial  meridian,  152. 

Celestial  sphere,  41,  42,  47. 

Cepheus,  48,  49,  108,  109. 

Ceres,  248,  250. 

Cetus,  49,  69,  71. 

Challis,  Professor,  270. 

Chamberlin  Observatory,  145. 

Chamberlin  telescope,  141. 

Chandler,  S.  C.,  125. 

Chinese  astronomy,  21,  93. 

Chromosphere,  189. 

Chronograph,  157,  171. 

Chronometer,  169. 

Clark,  A.  G.,  84,  307. 

Clocks,  146,  172. 

Clusters,  314. 

Coal,  179. 

Coma  Berenices,  89. 

Comet-groups,  274. 

Comet  hunters,  114,  271. 

Comets,  39,  271. 

Conjunction,  231,  237. 

Constellations,  48. 


337 


338 


Index. 


Copernicus,  26,  32,  212. 

Corona,  193,  230. 

Corona  Borealis,  92. 

Coronium,  195. 

Corvus,  91. 

Craters,  212. 

Cygnus,  98. 

Declination,  55. 

Declination  axis,  139. 

Deimos,  238. 

Delphinus,  104. 

Deneb,  98. 

Diameter  of  a  planet,  160. 

Diffraction  grating,  165. 

Dipper,  the  Great,  36,  60,  61. 

Dipper,  the  Little,  44,  61. 

Distance  of  the  sun,  181. 

Dollond,  John,  131. 

Dome,  148. 

Double  stars,  123,  160,  306. 

Draco,  99. 

Druids,  52. 

Duration  of  life  on  the  earth,  204. 

Earth  shine,  209. 

Eclipses,  224. 

Ecliptic,  51. 

Egyptians,  21. 

Ellipse,  273. 

Elongation,  232. 

Encke's  comet,  283. 

Envelopes,  276. 

Epicycles,  25. 

Equator,  celestial,  55. 

Equinox,  55,  69. 

Faculce,  189. 

Flamsteed,  54. 

Fomalhaut,  67. 

Galaxy,  see  Milky  Way. 

Galileo,  30, 128,  259. 

Galle,  270. 

Gauss,  248. 

Gemini,  79. 

Gould,  B.  A.,  116. 

Graduations,  150,  156. 

Gravitation,  33,  306. 

Great  Plague,  29. 

Grecian  philosophers,  22. 

Greek  alphabet,  55. 

Guinand,  131. 

Habitability  of  Mars,  245. 

Hall,  Asaph,  238. 


Hall,  Chester  Moor,  131. 

Heat  of  the  sun,  198,  201. 

Helium,  192,  323. 

Hercules,  53,  96,  315,  319. 

Herodotus,  21. 

Herschel,  Caroline,  64,  266. 

Herschel,  William,  35,  64,  265. 

Hesiod,  51. 

Hindus,  52,  229. 

Hipparchus,  23,  25,  86. 

Holden,  E.  S.,  114. 

Holmes's  comet,  282. 

Huyghens,  260. 

Hyades,  51,72,  74. 

Hydra,  92. 

Hyperbola,  273. 

Inferior  planets,  231. 

Inquisition,  31. 

Iroquois  Indians,  49. 

Josephus,  20. 

Judas  Iscariot,  210. 

Juno,  248,  250. 

Jupiter,  31,  39,  128,  202,  237,  250,  253, 

273,  328,  332. 
Kant,  327. 

Keeler,  James  E.,  121,  255,  263. 
Kepler,  29. 
Krakatoa,  217. 
Lacus  Solis,  243. 
Lagrange,  35. 
Lalande,  54. 
Laplace,  34,  286,  327. 
Laws,  Kepler's,  30,  33. 
Laws,  Newton's,  33,  34,  273. 
Leo,  86,  291. 
Leonids,  291,  294. 
Lepus,  85. 
Level,  151. 
Leverrier,  269. 
Lexell's  comet,  286. 
Libra,  103. 

Lick  Observatory,  155. 
Lick  telescope,  16,  259. 
Lippershey,  128. 
Lyra,  54,  95,  319. 
Madrid,  300. 
Magellanic  clouds,  326. 
Magnetic  storms,  199. 
Magnitudes  of  stars,  57. 
Mark  Twain,  204. 
Mars,  27,  29,  39,  236,  250,  329. 


Index. 


339 


Maxwell,  Clerk,  263. 

Mercury,  39,  231. 

Meridian  circle,  145,  149,  150,  152, 154. 

Meteoric  showers,  284,  290,  294. 

Meteorites,  293,  294. 

Meteors,  39,  288. 

Mexicans,  52. 

Micrometer,  124,  158,  272. 

Milk-dipper,  108. 

Milky  Way,  17,  18,  31,  38,  99,  301,  316, 

321. 

Mira,  72,  314. 

Mizar,  44,  45,  46,  60,  61,  62,  305. 
Moon,  36,  205. 
Motion  of  the  heavens,  36. 
Mountains  of  the  moon,  214. 
Mounting  of  a  telescope,  138,  139. 
Multiple  stars,  309. 
Nebulae,  39,  271,321. 
Nebular  theory-,  327. 
Neptune,  39,  268,  329,  332. 
Newcomb,  S.,  115. 
Newton,  Isaac,  32,  119,  125,  129,  130. 
Nova  Aurigae,  78,  312. 
Object-glass,  138,  153. 
Observatories,  143. 
Okouari,  49. 
Olbers,  248. 
Ophiuchus,  106. 
Opposition,  237. 

Orion,  39,  53,  74,  102,  321,  323,  325. 
Pallas,  248,  250.  » 

Parabola,  273. 
Par6,  280. 
Pegasus,  49,  64. 
Perihelion,  237. 
Periodicity  of  sun-spots,  186. 
Perseids,  290,  291. 
Perseus,  49,  81. 
Persians,  52. 
Personal  equation,  170. 
Peruvians,  52. 

Phases  of  inferior  planets,  232. 
Phobos,  238. 
Photography,  165,  329. 
Photosphere,  187. 
Piazzi,  247,  248. 
Pickering,  E.  C.,  60,  117. 
Pickering,  W.  H.,  119. 
Pisces,  68. 
Planetary  system,  39,  332. 


Pleiades,  37,  51,  72,  319,  323,  330. 

Pointers,  41. 

Polar  axis,  139. 

Pole,  celestial,  43,  62. 

Pole-star,  41,  61,  62. 

Pollux,  79. 

Procyon, 85. 

Prominences,  190,  230. 

Proper  motion,  319. 

Ptolemaic  system,  24. 

Ptolemy,  24,  59. 

Pythagoras,  22,  23. 

Radiant,  289. 

Red  spot  on  Jupiter,  255. 

Reflector,  130. 

Refraction,  218. 

Refractor,  131. 

Regulus,  86. 

Reticle,  151. 

Rigel,  75- 

Right  ascension,  55. 

"Rigveda,"  20. 

Rosse,  130. 

Sagitta,  100. 

Sagittarius,  109,  323. 

Satellites,  40. 

Saturn,  39,  259, 328,  332. 

Schseberle,  J.  M.,  197. 

Schiaparelli,  233/240,  241. 

Schwabe,  186. 

Scientific  method,  20. 

Scorpio,  101. 

Serpens, 106. 

Serpentarius,  see  Ophiuchus. 

Sextant,  223. 

Shadow  of  the  earth,  15. 

Shooting  stars,  288. 

Showers,  meteoric,  284,  290,  294. 

Sirius,  36,  37,  53,  74,  §4,  304,  3°7- 

Site  of  an  observatory,  143. 

Society  Islanders,  51. 

Solstice,  79. 

Spectroscope,  162. 

Spectrum  analysis,  163. 

Sphere,  celestial,  41,  42,  47. 

Spica,  90,  91,  309. 

Spider-webs,  161. 

Standard  time,  168,  174. 

Star-light,  305. 

Starry  skies,  15. 

Stars,  38,  301. 


340 


Index. 


Structure  of  the  universe,  318. 

Sun,  179. 

Sun-spots,  182. 

Superior  planets,  237. 

Swift,  Lewis,  230,  287. 

Swift's  comet,  278. 

Taurus,  54,  72. 

Telescope,  128,  141. 

Temporary  stars,  311. 

Tides,  205,  223. 

Time,  117,  167,  223. 

Transit,  231. 

Trapezium,  76,  325,  330. 

Tycho,  28,  29,  32,  63,  311. 

Types  of  stellar  spectra,  309. 

Uranienburg,  29. 

Uranus,  39,  247,  265,  268,  329,  332. 

Ursa  Major,  59. 


Ursa  Minor,  61. 

Variable  stars,  310,  311. 

Vega,  36,  37,  62,  95,  305. 

Venus,  31,  37,  38,  39,  128,  231,  234,  253. 

Vernal  equinox,  55,  69. 

Vesta,  248,  250. 

Vesuvius,  215. 

Virgo,  90,  104. 

Volcanoes,  215. 

Watches,  176. 

Watson,  J.  C.,  230. 

Weather,  201,  225. 

Weigel,  Professor,  50. 

World's  Fair,  211,  296. 

Yerkes  Observatory,  144. 

Young,  Charles  A.,  112,  191,  200. 

Zodiac,  50,  51. 

Zodiacal  light,  294. 


14  DAY  USE 


STATISTICS  UIRARY 


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